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CERC WAVE GAGES 





TECHNICAL MEMORANDUM NO. 30 
DECEMBER 1969 




Ifl^ U. S. ARMY, CORPS OF ENGINEERS 

. m^ COASTAL ENGINEERING 
mi^ RESEARCH CENTER 



This document has been approved for public release and sale; 
its distribution is unlimited. 



Reprint or republication of any of this material 
shall give appropriate credit to the U. S. Army Coastal 
Engineering Research Center. 

Limited free distribution within the United States 
of single copies of this publication is made by: 

Coastal Engineering Research Center 
5201 Little Falls Road, N.W. 
Washington, D. C. 20016 



Contents of this report are not to be used for 
advertising, publication, or promotional purposes. 
Citation of trade names does not constitute an official 
endorsement or approval of the use of such commercial 
products . 



The findings in this report are not to be construed 
as an official Department of the Army position unless 
so designated by other authorized documents. 



CERC WAVE GAGES 



by 
Leo C. Williams 



TECHNICAL MEMORANDUM NO. 30 
DECEMBER 1969 




H° U. S. ARMY, CORPS OF ENGINEERS 

™ COASTAL ENGINEERING 
RESEARCH CENTER 



This document has been approved for public release and sale; 
its distribution is unlimited. 



ABSTRACT 

CERC has used wave gages to gather prototype wave data since 1948. 
Two basic types of gages are now used in the field - the step-resistance 
staff gage and the underwater pressure-sensitive gage. CERC has developed 
three types of step-resistance staff gages - a series type for use in 
fresh water, a parallel type for use in salt water, and a relay-operated 
type for use in either fresh or salt water or in water where wide changes 
in salinity occur. The pressure gage can be used in water of any salinity. 
The series and parallel gages have an accuracy of ±5 percent plus the 
spacing of one sensor increment. The relay gage has an accuracy of ±2 
percent plus the spacing of one sensor increment. The accuracy of the 
pressure-sensitive gage is not as precise as that of the step-resistance 
gages . 

The report describes each gage and the theory of operation, details 
of fabrication, steps for calibration and installation, and requirements 
of maintenance. 



FOREWORD 

This report describes in detail the sensors and recorders used by 
CERC in wave-data collection programs. Leo C. Williams, Chief of the 
Instrumentation and Equipment Branch, Research Division, prepared this 
report and developed most of the wave-data equipment used at CERC. 
Thorndike Saville, Jr. is Chief of the Research Division. The 
manuscript was prepared in 1966. 

Many drawings in this publication have been greatly reduced from 
the originals. The large originals are available at CERC in limited 
quantities . 

At the time of publication. Lieutenant Colonel Edward M. Willis 
was Director of the Center; Joseph M. Caldwell was Technical Director. 



NOTE: Comments on this publication are invited. Discussion will be 
published in the next issue of the CERC Bulletin. 



This report is published under authority of Public Law 166, 79th 
Congress, approved July 31, 1945, as supplemented by Public Law 172, 
88th Congress, approved November 7, 1963. 



CONTENTS 

Page 

Section I. INTRODUCTION 1 

1 . Wave Program at CERC 1 

2. Recording and Analysis 1 

3. Types of Wave Gages 2 

Section II. SERIES-TYPE, STEP-RESISTANCE GAGE FOR USE IN FRESH 

WATER 9 

1. Theory of Operation of Series-Type, Step-Resistance Gage .. 9 

2. Fabrication of Series-Type, Step-Resistance Gage 16 

3. Operation of a Series-Type, Step-Resistance Wave Gage ... 20 

Section III. PARALLEL -TYPE, STEP -RES I STANCE GAGE FOR SALT WATER . . 28 

1. Theory of Operation of Parallel-Type, Step-Resistance Gage 28 

2. Fabrication of a Parallel -Type, Step-Resistance Gage ... 34 

3. Operation of Parallel-Type, Step-Resistance Gage 40 

Section IV. RELAY-TYPE, STEP-RESISTANCE GAGE FOR SALT AND FRESH 

WATER • 45 

1. Theory of Operation of a Relay- Type, Step-Resistance Gage . 45 

2. Fabrication of a Relay-Operated Step-Resistance Gage ... 47 

3. Operation of a Relay-Type, Step-Resistance Gage 59 

Section V. PRESSURE-SENSITIVE GAGE 63 

1. Theory of Operation of Pressure-Sensitive Gage 63 

2. Fabrication of a Pressure-Sensitive Gage 64 

3. Operation of Pressure-Sensitive Gage 73 

Section VI. FABRICATION OF EPOXY GAGE SECTION 79 

Section VII. MAGNETIC TAPE RECORDER FOR OCEAN-WAVE GAGES 83 

1. Theory of Operation of Magnetic Tape Recorder 83 

2. Fabrication of Magnetic Tape Recorder 85 

3. Calibration and Operation 93 

Section VIII. MODIFICATION OF STRIP-CHART RECORDER SPEED 101 

Section IX. ANALYSIS OF OCEAN-WAVE GAGE RECORDS Ill 

1. Step-Resistance Wave Gages Ill 

2. Pressure-Sensitive Gages 116 



iir 



ILLUSTRATIONS 

Tables Page 

I Resistance Values in Ohms for 20-Foot Gage for Fresh Water 12 

II Resistance Values in Ohms for 25-Foot Series Gage 13 

III Components for 25-Foot Five-Section Fresh-Water 

Series-Resistance Gage 15 

IV List of Components for Wave-Gage Holder 22 

V Resistor Values for Salt-Water Parallel Step-Resistance 

Wave Gage 31 

VI Components for Five-Section 25-Foot Parallel Resistance 

Gage for Salt Water 32 

VII Components for Five-Section 25-Foot Relay Staff Gage ... 55 

VIII Resistor Values in Ohms for 125-Point Relay Gage 58 

IX List of Components for Pressure-Sensitive Gage, Model BE-2. 66 

X List of Components for Magnetic Tape Recorder, LW-1 .... 86 

XI Parts Required for a Calibration Unit for Calibration of 

a Tape Recorder with a Strip-Chart Recorder 96 

Figures 

1. Block Diagram of Series-Type Step-Resistance Gage for 

Fresh Water 4 

2. Block Diagram of Parallel Step-Resistance Gage for Salt Water 5 

3. Block Diagram of Relay-Operated Step-Resistance Gage ... 6 
4- Block Diagram of Pressure-Sensitive Wave Gage 7 

5. Series-Type, Step-Resistance Gage for Fresh Water 9 

6. Series-Type, Step-Resistance Gage for Fresh Water. 10 

7. Practical Circuit for Measuring Wave Heights in Fresh Water 14 

8. Series-Type Step-Resistance Wave Gage for Use in Fresh Water 17 



Figures Page 

9. Power lonit for Fresh-Water Staff Gage 18 

10. Progranuner for Wave Gages 19 

11. Signal Input Cable for Strip-Chart Recorder 19 

12. Holder for Sectional Step-Resistance Gage Sections .... 23 

13. Pile Clamp for Wave Gage 24 

14. Diagram of Fresh-Water Staff Gage 25 

15. Wiring Diagram for Fresh-Water Gage Section 26 

16. Functional Block Diagram of Parallel-Type, Step-Resistance 

Gage for Salt Water 29 

17. Functional Diagram for Parallel Resistor Gage 30 

18. Parallel -type, Step-Resistance Gage for Use in Salt Water . 35 

19. Transformer Unit for Salt -Water Gage 36 

20. Wiring Diagram of Transformer Unit of Parallel Step- 

Resistance Gage 37 

21. Panel Assembly for Parallel-Resistance Gage 38 

22. Wiring Diagram for Power Supply and Programmer of Parallel 

Step-Resistance Gage 39 

23. Connecting Diagram for Parallel Step-Resistance Gage Section 41 

24. Hookup Diagram for Parallel-type Step-Resistance Gage ... 42 

25. Simplified Diagram of Relay-type, Step-Resistance Gage . . 46 

26. Modified Circuit for Relay-type, Step-Resistance Gage ... 46 

27. Simplified Diagram for Relay Gage 48 

28. Relay-Operated Step-Resistance Wave Gage for use in 

Fresh or Salt Water 49 

29. Relay-panel Layout for Relay-type Gage 50 

30. Front Panel and Chassis Drilling for Relay-type Gage ... 51 

31. Relay Panel - A, B, C, D, E 52 



V 



Figures Page 

32. Power Supply for Relay Staff Gage 53 

33. Cabinet Assembly for Relay-type, Step-Resistance Gage . . 54 

34. Block Diagram for Relay Staff Gage 60 

35. Parts and Assembly Drawing of Pressure-Sensitive Gage . . 65 

36. Washers for Blocking Bellows of Pressure Gage 68 

37. Power Supply Unit for Amplifier of Pressure-Sensitive Gage 70 

38. Amplifier Power-Supply Unit for Pressure Gage 71 

39. Concrete Block for Mounting Pressure-Sensitive Gage ... 72 

40. Diagram for Pressure-Sensitive Gage 76 

41. Patterns, Container, and Molds for Epoxy Sections for 

Step-Resistance Gages 80 

42. Parts for Magnetic Tape Recorder, LW 1 88 

43. Magnetic Tape Recorder Panel Layout, Model LW-1 89 

44. Chassis Layout for Model LW-1 Magnetic Tape Recorder . . 90 

45. Chassis Layout for Model LW-1 Magnetic Tape Recorder . . 91 

46. Schematic Diagram for Magnetic Tape Recorder, Model LW-1 92 

47. Calibration Signal Timer for Magnetic Tape Recorder ... 94 

48. Diagram of Calibration Unit 95 



49. Magnetic Tape Recorder, Model LW-1 

50. Block Diagram of Calibration Hookup 

51. Wave Records with Chart Speed of 2.5 mm per second 

52. Wave Records with Chart Speed of 1.25 mm per second 

53. Wave Records with Chart Speed of 1.0 mm per second 



97 

99 

102 

103 

104 



54. Gear Modification of Brush Recorder Chart Drive to 

furnish chart speeds of 2.5, 12.5, 62.5 mm per second . 105 



Figures Page 

55. Gear Modification of Brush Recorder Chart Drive to furnish 

chart speeds of 1.25, 6.25, or 31.25 mm per second . . . 106 

56. Gear Modification of Brush Recorder Chart Drive to 

furnish chart speeds of 1.0, 5.0, 25.0 mm per second . . 107 

57. Gear Train Brush Recorder prior to modification 109 

58. Gear Train Brush Recorder after Modification 110 

59. Sample Wave-period Template 112 

60. Sample of Wave-height Template 113 

61. Sample of Wave-height Template ........ 114 

62. Wave-data Compilation Sheet 115 

63. Pressure Response Curves for Various Depths and Wave 

Periods 116 



VII 



Section I. INTRODUCTION 

1. Wave Program at CERC 

The Coastal Engineering Research Center (CERC) , formerly the 
Beach Erosion Board, has been collecting data from wave gages for more 
than 20 years. The program started in April 1948, when the first gages 
were installed in New Jersey. Since then, many gages have been installed. 
In addition to gages on the Atlantic, Gulf of Mexico, and Pacific shores, 
gages have been installed in the Great Lakes, at Hawaii, and in smaller 
inland lakes and reservoirs. 

Signals from 7 locations and 10 gages are now instantaneously re- 
corded on a central panel in the CERC Laboratory. These signals are 
carried by leased telephone lines. 

CERC uses two basic types of wave gages - the step-resistance staff 
gage and the pressure-sensitive gage. The more accurate is the step- 
resistance gage and it is favored for use in locations where a structure 
is available for its installation or where the construction of a suitable 
support is feasible. The pressure-sensitive underwater gage is selected 
for those sites where a less accurate gage is acceptable for a measure- 
ment program, and where the measurement of waves with periods of less 
than 4 seconds is not required. 

2. Recording and Analysis 

Recordings from both types of gages are normally produced on a 
pen and ink paper strip-chart recorder. The length of time that the 
waves are recorded is selected in accordance with the mission of the 
individual gage or within the overall program of wave study. Automatic 
programming of the gage recording time is normally provided along with 
a control for manual selection of special recording periods. 

Tide changes are not normally removed from the strip-chart record- 
ings taken with the staff type step-resistance wave gage. However, tide 
removal can be provided for this gage should the requirement for this 
type operation arise. Tide changes are removed from the pressure- 
sensitive wave gage. If such removal was not incorporated in the gage 
operation, barometric changes would also be present in the recording, 
thus a record that would be difficult to analyze would be produced. 

Data from both types of wave gages may be recorded on magnetic tape. 
Records made on magnetic tape are analyzed on a spectrum analyzer in the 
CERC Laboratory. The analyzer performs the following analyses from a 
20-minute recording: 

a) Linear average wave height. 

b) Squared average wave height. 

c) Linear peak wave height. 



d) Squared peak wave height . 

e) Linear integrated wave height. 

f) Squared integrated wave height. 

These values are presented on the vertical axis of the spectral 
plot with the corresponding wave period presented on the horizontal 
axis of the plot. 

The magnetic tape recorder usually records wave conditions continu- 
ously using a tape speed of 1/2 inch per minute. One roll of 1/4 inch 
wide magnetic tape 1,250 feet long, records continuously for approximately 
3 weeks. 

The magnetic tape recorder has a built-in calibration generator (sine 
wave) with a period of 4 seconds. The calibration signal is adjusted to 
provide an amplitude equal to that produced by the wave gage for full- 
scale recording on the strip chart and magnetic tape. This calibration 
signal is recorded for 30 minutes every 12 hours to provide a standard- 
ization signal to compensate for changes found in magnetic tape from roll 
to roll, and to calibrate the entire spectrum analyzer in the laboratory. 
The calibration signal is timed by a program clock connected with the 
tape recorder. 

3. Types of Wave Gages 

The staff type step-resistance wave gage is available for three 
different applications: 

a) Series step-resistance type for use in fresh water. 

b) Parallel step-resistance type for use in salt water loca- 
tions where little or no change occurs in salinity. 

c) Relay-operated step-resistance type that will operate in 

either fresh water or salt water and where wide changes 
in salinity occur. 

The accuracy of the recording taken with the fresh-water, series, 

step-resistance gage and the salt-water, parallel, step-resistance gage 

is about plus or minus 5 percent, plus the spacing of one staff-sensing 
point. 

The accuracy of the recording taken with the relay-operated step- 
resistance gage is about plus or minus 2 percent plus the spacing of one 
staff sensing point. Due to the increased accuracy expected of this gage, 
servicing and cleaning of the sensing elements may have to be performed 
more often than on the other two step-resistance gages. This service 
will depend on local conditions of sea growth at the gage site. 

The sensing units for the staff type step-resistance wave gages are 
molded from epoxy resin in 5-foot lengths, and are stacked in a steel or 



alvuninum holder to provide the gage length desired for the location, 
usually 15 to 25 feet. Sensing contacts are molded into the 5-foot 
sections at intervals to provide the incremental accuracy required 
of the gage. Sensing contacts spaced every 0.2 foot have been found 
adequate for gages with lengths of 15 to 25 feet. Sensing contacts 
spaced 0.1 foot have been used on gages of 10 feet or less. 

The sensing unit for the pressure-sensitive underwater wave gage 
senses the change in pressure produced by the increase (or decrease) in 
water height as the wave passes over the gage. The change in pressure 
produced by a wave with an 8-second period with a height of 4 feet on a 
gage submerged in 30 feet of water will be less than that produced by 
the same wave on the same wave gage submerged in 10 feet of water. A 
wave with a period shorter than 8 seconds and with a height of 4 feet 
will produce less pressure at both the 30-foot and 10-foot depths than 
the 8-second wave. This phenomena is referred to as a pressure gradient 
condition produced as a function of wave height versus wave period versus 
water depth to the sensing element. 

The pressure-sensing element used by the CERC is designed for use 
in locations where the total water depth (stillwater depth plus height 
of wave crest) is less than 50 feet. Sensing elements with similar 
characteristics that are interchangeable with the CERC model except for 
the d.c. power requirements are available from commercial sources. One 
of these is Fairchild Semi-Conductor Corporation Model TF 150 series. 
These sensors are available in a variety of pressure ranges and may be 
used in water depths greater than the 50-foot total range of the CERC 
model. However, use of a pressure-sensitive gage in water depths greater 
than 30 feet is not advised due to the depth-period attenuation factor 
of recordings taken from such an installation. 

Figure 1 shows a block diagram of the components used in a series- 
type step-resistance wave gage for use in fresh water. 

Figure 2 shows a block diagram of a parallel-type step-resistance 
wave gage for use in salt water. 

Figure 3 shows a block diagram of a relay-operated step-resistance 
wave gage for use in water of varying salinity. 

Figure 4 shows a block diagram of a pressure-sensitive wave gage. 



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Section II. SERIES-TYPE, STEP -RESISTANCE GAGE FOR USE IN FRESH WATER 

1, Theory of Operation of Series-Type, Step-Resistance Gage 

The series- type, step-resistance gage operates on the principle 
of a simple series-type circuit with a constant voltage d.c. source, a 
recorder penmotor and a variable resistor connected in series. Figure 5 
shows a simple series circuit containing a constant voltage source, the 
penmotor, and a variable resistance. 



CONSTANT VOLTAGE 




RECORDER 




Recorder Pen 


(DC. Source) 


PEN MOTOR 
























N^<^ 









Variable Resistor 

Figure 5. Series-Type, Step-Resistance Gage for Fresh Water 



The recorder penmotor is essentially the same as an ordinary 
D'Arsonval panel-meter movement with a capillary, ink pen substituted 
for the indicating pointer. The components (magnet, moving coil, springs, 
etc.) are significantly larger and more rugged than the ordinary meter 
movement . 

The variable resistor used in a gage consists of several fixed re- 
sistors in series with contact tips connected to the resistor junctions. 
The contact tips are molded into long epoxy resin shapes that allow the 
contact tips to be exposed. The number of contacts submerged by the 
part of the gage that is under water forms the variation in resistance. 

The constant voltage d.c. source is obtained from a transformer, 
rectifier, filter, and voltage regulator operated from a 115-volt, 60- 
cycle power line. The output voltage from these components is constant 
even though the input line voltage may vary from about 95 to 130 volts 
and thus prevents the recorder penmotor from changing with a varying 
line voltage. 

Since the voltage source is constant and the resistance of the pen- 
motor is constant (neglecting temperature changes) , the current in the 
circuit will increase if the value of the variable resistor is decreased. 
Ohms law, E = IR, applies. 



The recorder penmotor is designed to provide a linear pen movement 
with a linear change in input current . 

The nominal current required to move the penmotor pen through a 50- 
millimeter arc (full scale) is 20 milliamperes. The penmotor has a 
nominal internal resistance of 1,500 ohms, thus by ohms law the constant 
voltage source will be a nominal 30 volts (E = IR; .02 x 1,500 = 30 volts) 
for the required pen movement. 

To make the penmotor move in equal increments from a variable resis- 
tor made of several resistors connected in series as shown in Figure 6, 
it is necessary to calculate each individual resistor value. 



CONSTANT VOLTAGE 
(DC. Source) 




RECORDER 
PEN MOTOR 




















K K 1 K 2 R 3 










• • • () 

Movahip Contnrt 





Figure 6. Series-Type, Step-Resistance Gage for Fresh Water. 

Assuming a wave gage with 20 equal measurement increments and a pen- 
motor with an internal resistance of 1,500 ohms that requires 20 milli- 
amperes for full-scale movement and that indicates linearly with a change 
in current, then to move the pen full scale, 20 current changes of 1 
milliampere each would be required. A 30-volt power source would provide 
full-scale penmotor movement. 



30 volts 
1,500 ohms 



,02 amperes 



The first of the 20 intervals of gage measurement would reduce the 
20-milliampere penmotor current by 1 milliampere. 

To calculate the first gage resistor: 

30 volts 



19 milliamperes 



1,579 ohms. 



1,579 ohms total circuit resistance minus 1,500 ohm penmoter resistance 
79 ohms (first resistor) . 



10 



To calculate the second resistor value: 

30 volts ^ 1,667 ohms - 1,579 = 88 ohms. 

18 milliamperes 

To calculate the third resistor: 

30 volts 



17 milliamperes 



1,765 ohms - 1,667 ohms = 98 ohms, 



Such calculation shows that the resistors will not be of equal value 
to obtain equal increments of pen movement. The individual resistor values 
will be higher at the left and lower on the right side of the resistor 
string in Figure 6. 

The circuit in Figure 6 applied to a practical circuit for measuring 
wave heights in fresh water is shown in Figure 7. 

The major difference between the two circuits (Figures 6 and 7) is 
that the water path is now used to activate the changes in the variable 
resistor. Another change is the addition of a variable calibration re- 
sistor to adjust for differences in the conductivity of fresh water and 
differences in penmotors. Analysis of this circuit shows that the bottom 
resistor in the gage circuit is connected to the ground rod. This con- 
nection is necessary due to the electrical resistance of the residual water 
path on the epoxy resin when the gage submergence is small. Further analy- 
sis of the circuit shows that the water path has a resistance of its own, 
therefore, some current will flow from each submerged metal sensing tip to 
the ground rod; such flow will aid in reducing the effective resistance 
of the water path. 

Using the 30-volt source previously calculated as required to provide 
full-scale penmotor operation in the practical gage circuit in Figure 6, 
it is found that the recorder penmotor will not rise to full scale. This 
is due to the added resistance of the water path. To compensate for the 
increased resistance, it is necessary to increase the voltage from the 
constant d.c. voltage source. The increased resistance path will also 
change the direct logic used for Figure 6 in calculating the resistors for 
the gage. 

Design experience has resulted in the selection of a d.c. voltage 
source of 46 and 54 volts as the best value for most fresh-water applica- 
tions. This same experience has resulted in the resistor values shown in 
Tables I and II for 20- and 25-foot series-type gages. If a 10-foot gage 
is desired, it is recommended that the spacing of the sensing tips be used 
to 0.1 foot and the resistor values for the 20-foot gage be used. 

There will be some electrolytic action in the water path due to the 
use of direct current. This action usually causes a hard powder to form 
on the lead sensing tips of the gage. Rate of coating formation depends 
on the mineral content of the local water. The gage must be cleaned of 
the deposit to obtain the most accurate operation. Frequency of cleaning 

Text resumes on page 16 



CONSTANT VOLTAGE 
(D.C. Source) 



Ground Rod 



Water, 
Level 



RECORDER 
PEN MOTOR 



-Wi/^V- 



Vorioble Calibration Resistor 



Metal Sensing Tips 



Recorder 



Pen 



Individual Resistors Molded 
into Epoxy Resin Wove 
Staff Units. 




Figure 7. Practical circuit for measuring wave heights in fresh water. 



12 







TABLE 


± 






RESISTANCE 


VALUES IN 


OHMS FOR 


20- FOOT 


GAGE FOR 


FRESH WATER 


Top 
Section A 


Section B 


Section C 


Bottom 
Section D 


24 


41 




83 




267 


24 


41 




87 




286 


24 


42 




90 




305 


25 


43 




93 




326 


26 


45 




96 




351 


26 


45 




101 




377 


26 


47 




104 




408 


27 


48 




109 




441 


28 


50 




113 




480 


28 


50 




118 




522 


29 


53 




123 




572 


29 


53 




129 




629 


30 


55 




134 




695 


30 


57 




141 




771 


31 


59 




147 




861 


32 


60 




155 




968 


33 


62 




162 




1096 


33 


64 




171 




1251 


34 


67 




179 




1441 


35 


68 




189 




1678 


36 


70 




200 




1980 


37 


73 




210 




2370 


38 


75 




224 




2888 


38 


78 




236 




3598 


39 


81 




252 


T 


4606 


7W^ 


5^, fDicI 



13 









TABLE II 








RESISTANCE 


VALUES 


IN OHMS FOR 25-FOOT 


SERIES GAGE 




No. 


Top 
Section A 


Section 


B Section C 


Section D 


Bottom 
Section E 


1 


22 


33 


55 


110 


324 


2 


21 


34 


56 


115 


343 


3 


23 


34 


59 


118 


365 


4 


23 


35 


59 


123 


387 


5 


24 


36 


61 


128 


412 


6 


23 


36 


62 


131 


441 


7 


25 


37 


64 


137 


471 


8 


24 


38 


66 


142 


504 


9 


25 


38 


67 


147 


543 


10 


25 


39 


70 


154 


585 


11 


26 


40 


71 


159 


632 


12 


26 


41 


73 


166 


686 


13 


26 


42 


75 


173 


746 


14 


27 


42 


77 


180 


814 


15 


27 


44 


79 


188 


894 


16 


28 


44 


81 


197 


983 


17 


28 


45 


84 


205 


1089 


18 


29 


47 


87 


215 


1212 


19 


29 


47 


88 


226 


1357 


20 


30 


48 


92 


236 


153t) 


21 


30 


50 


95 


249 


1738 


22 


31 


50 


97 


261 


1961 


23 


32 


51 


101 


275 


2334 


24 


32 


53 


103 


291 


2698 


25 


32 


55 


108 


306 


3201 



14 



TABLE III 
COMPONENTS FOR 25-FOOT FIVE-SECTION FRESH-WATER SERIES-RESISTANCE GAGE 

1. Strip-Chart Recorder Brush #RD-2321-00. Order with following 1 ea. 
modifications: single channel operation with 50 ram chart width. 

Old style penmotor #BL 902 and long pen #BL 921. 

2. Chart rewind Brush #RA-2402-10 1 ea. 

3. Constant voltage power supply 48-52 volts 100 ^dA Technipower 
#M-50.0 - 0.100, or equal. 

4. Toggle Switch SPST AH§H #20994-BF 2 ea 

5. Potentiometer 1.5K Mallory #M1.5MPK, or equal 1 ea. 

6. Potentiometer 2K Mallory M2MPK, or equal 1 ea. 

7. Relay Potter Brumfield #KR HAG, or equal 1 ea. 

8. Plug amphenol #80 PC2F, or equal 2 ea. 

9. Plug amphenol 80 MC2M 2 ea. 

10. Cord set Belden 17408-SJ, or equal 3 ea. 

11. Binding post, Superior type DF30 black 1 ea. 

12. Binding post, Superior Type DF 30 red 1 ea. 

13. Aluminum chassis Bud #AC-411, or equal 1 ea. 

14. Time switch Tork Hourmaster #4100, or equal 1 ea. 

15. Socket amphenol #160-10 3 ea. 

16. Epoxy resin Scotchcast #2 42 lbs. 

17. Precision Resistors Wirewound 190 type TX 2212 Precision 125 ea. 
Resistor Co. 109 U.S. Highway, Hillside, N.J., (see 

Tables 1 and II) . 

18. Cable 2-conductor #20 AWG with 2 High-strength steel members. 110 ft. 
Neoprene outer sheath. Marsh ^ Marine Co. Houston, Texas, 

Type #TPSC, or equal. 

19. Bar solder 50/50 tin-lead for lead sensing tips 6 lbs, 

20. Bare copper wire tinned #18 AWG 50 ft. 

21. Cable 2-conductor #16. Length as required to connect wave 
staff site to recording site. 

NOTE; Steel "H" beam is needed for holder for epoxy gage sections. 



15 



must be determined locally for each gage. Reversing the two electrical 
leads connected to the wave staff will reverse the polarity of the voltage 
to the staff, and may aid in changing the electrolytic action, and extend 
the periods of operation between cleanings. 

The lead sensing tips of the epoxy gage sections are extended from 
the main body of the section to increase the insulating distance provided 
by the epoxy resin between the sensing tip and the metal gage mount. This 
increased distance helps to increase the resistance value of the water 
film remaining on the epoxy resin after a wave crest has passed, thus 
providing the desired stepped resistance change by the rising and falling 
action of the water during wave action. 

The penmotor will move in proportion to the stepped resistance changes 
in the wave staff, and will provide a profile of the water surface against 
time on the moving strip- chart on the recorder. 

The series-resistance gage will operate most accurately in locations 
where small changes occur in the mineral content of the water. If the 
gage is operated during conditions where great changes in mineral content 
occur, such as during periods of large snow runoff, the gage calibration 
should be checked during such conditions, and the recordings corrected 
as necessary. 

2. Fabrication of Series-Type, Step-Resistance Gage 

Most of the parts needed for fabrication are listed in Table III. 
The desired number of epoxy gage sections are molded as shown on Figure 8. 
Cables for each section should be long enough to allow submerging all gage 
sections at one time while working from the top of the gage mount. This 
will allow operating personnel to calibrate the gage at regular intervals. 
The top gage section has the lowest resistor value between the top plug 
and the second plug. Resistors increase in value from the top of the 
gage toward the bottom, the highest value of resistance being between the 
bottom plug and the connecting conductor molded into the gage. 

The power supply requires the small aluminum chassis and the parts 
indicated on Figure 9. Layout of the power supply is not critical, use 
of good shop practice' is all that is required. The voltage-adjust control 
on the constant voltage power module must be available for adjustment. 

Three 115-volt receptacle plugs, one line cord and one toggle switch 
are installed in the sides of the timer. These items are installed and 
wired as shown in Figure 10. 

The strip-chart recorder listed in the parts list (Table III) for 
this gage has a minimum chart speed of about 12 inches per minute. To 
save chart paper, the recorder can be modified for a chart speed of 6 
inches per minute. This modification is recommended and is outlined in 
Section VIII. A connecting cable to this recorder from its input signal 
connector is made in the desired length using 2-conductor No. 18 cable 
as shown on Figure 11. 

16 



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18 



Tork Timer No. 4100 



Line Cord 
Belden I7408S 




Clock Motor Winding 



Clock Switch 



v^l 



/ Manuol Switcti 
AHSH 20994-BF 



Amptienol Plugs 
No. 160-10 



Ground green conductor in coble and 
grounding terminal in amphenol plugs 
to timer cose. 

Figure 10. Programmer for Wave Gages. Plugs and switch to be mounted in 
right side and bottom of case as mechanically feasible. 
(Do not mount on lid.) • 



Connector Amphenol Connector Type 

80MC2M AN3I08B-I4S-6S 





2 Conductor, No. I8AWG Coble. 
Length os Desired (6-8 ft.) 

Figure 11. Signal Input Cable for Strip-Chart Recorder. 

19 



The metal wave-gage holder is fabricated to the desired length as 
shown in Figure 12; a list of components used in fabrication is shown in 
Table IV. Mounting brackets for attaching the holder to the supporting 
structure should be strong enough to support the holder during severe wave 
conditions. Figure 13 outlines one type of bracket that has been used in 
supporting the gage holder on a vertical piling. The gage holder gets two 
coats of zinc chromate primer and two or three coats of anti-fouling paint 
as used on ship bottoms. Government agencies may use this paint which is 
available through Government Services Administration (GSA) supply - Stock 
No. GS8010-550-8305 for the primer and Stock No. GS8010-290-6651 for the 
anti-fouling paint. DO NOT PAINT THE GROUND ROD. Install the ground rod 
after the gage holder has been installed. The holders should be installed 
so that about 6 to 8 feet are below mean lower low water, 17 to 19 feet 
out of the water. 

Only the epoxy wave gage sections that are below or at the water 
line require anti-fouling paint. Mold release must be removed from the 
gage sections prior to painting. DO NOT PAINT THE LEAD SENSING TIPS. 

3. Operation of a Series-Type, Step-Resistance Wave Gage 

a. Installation 

When placing the epoxy wave gage sections in the gage holder, 
the section having the highest value resistors is the bottom section, and 
goes into the holder first. The section with the next highest value re- 
sistors is placed in the holder on top of this section, and so on until 
the section having the lowest value of resistors is in the top of the 
gage holder. 

The power unit, the strip-chart recorder, program clock, magnetic 
tape recorder (if used) and chart rewinder are connected as shown on 
Figures 14 and 15. 

b. Calibration 

The accuracy of the recorded wave heights will depend directly 
on the accuracy of the calibration of the gage. There will be enough dif- 
ference in each wave gage and in each strip- chart recorded to require that 
each gage be individually calibrated. 

The ideal calibration would be raising and lowering the gage holder 
with the gage sections into the water in small increments and marking the 
strip-chart recorder with each move. Usually, lack of water depth, the 
manual process required, and the presence of wave action prevent such 
calibration. 

If many gages are to be calibrated, it may be desirable to provide 
a cistern- like basin about 24 inches in diameter with the required depth. 
A wave gage holder would be a permanent part of the calibration pit. Such 



20 



a pit should be made of concrete pipe or other nonconducting material; 
use of a metal wall would cause an inaccurate calibration of the gage. 

The procedure outlined below has been satisfactorily used for cali- 
bration of staff-type gages. If feasible, a time of low-wave action 
should be selected for the calibration. 



If possible, the sections that are to be removed from the water first 
are kept inside the steel gage holder. This provides a more accurate gage 
calibration. If the water is deep enough, place two or three of the sec- 
tions in the holder in the order that they are used in the gage. The 
section having the lowest value of resistors is on top, and the succeed- 
ing sections are below it. When the section having the lowest value of 
resistors has been removed from the holder (in the desired calibration 
increments) , the other gage sections in the holder should be removed, and 
a succeeding section should be put in the bottom of the mount, thus all 
sections having the lowest resistors will be removed from inside the gage 
holder in succession during the calibration process. 

Calibration of the gage proceeds as follows: 

If a magnetic tape recorder is used, calibrate it with 
the strip-chart recorder as outlined in Section VII. 

Turn the strip-chart recorder "on-off" switch to "off". 

Turn the "off-on" power switch on the power supply unit 
to "on". 

Remove all epoxy wave gage sections from the metal gage 
holder. 

Turn on the strip-chart recorder using the switches on 
the recorder and on the programmer. 

Using the mechanical lever on the recorder penmotor, adjust 
the recording pen to the left side of the chart paper. 

Place the epoxy gage sections under water being careful to 
keep the lead tips adjacent to the metal gage holder with 
about the same spacing from the ground rod as they would 
have been installed in the gage holder. 

Adjust the calibration resistor on the power unit to 
provide full-scale reading on the strip-chart recorder. 



Remove all wave gage sections from the water. 

Repeat steps f, g, h, and i until zero and full scale are 
obtained. 

Text resumes on page 27 



21 



TABLE IV 



LIST OF COMPONENTS FOR WAVE-GAGE HOLDER (FIVE-SECTION, 25-FOOT GAGE) 

1. Steel "H" Beam 4" x 4" WF-I3 pounds per foot, 25 feet long 1 each 

2. Steel rod 1/2" diameter 25 feet long, hot rolled 5 

3. Steel rod 3/8" x 1/2", 25 feet long, hot rolled 2 

4. Steel rod 3/8" x 1/2", 10 feet long, hot rolled 

5. Steel rod 1/2" x 1/2'; 20 feet long, hot rolled 

6. Steel plate 3/8" x 6" 20 feet long, hot rolled 

7. Steel plate 1/2" X 8" , 3 feet long, hot rolled 

8. Steel bar 1" x 3", 7" long, hot rolled 

9. Steel bar 1" x 2", 4" long, hot rolled 

10. Cap screws, type 316 stainless steel, 5/8" x 6" long, 10 
11 threads per inch Hex head 

11. Cap screw, type 316 stainless steel, 5/8" x 1 3/4" long 20 
1] threads per inch Hex head. 

12. Cap screw, type 316 stainless steel 5/8" x 3 1/2" long 17 

13. Lock washer, type 316 stainless steel for 5/8" bolt 45 

14. Nuts, type 316 stainless steel, 5/8" regular, 11 threads 45 
per inch. Hex head. 



NOTE: Mounted to 8- inch Steel "H" beam pile as supporting structure, 



22 




23 




u 
o 



24 



115 V 



II5V 



Gage Coble 




II5V 



Note: Wove goge connect os shown 
on Figure 15 



CHART 
REWIND 



Figure 14. Diagram of Fresh-Water Staff Gage. 



25 



No. 14 or 16 AWG Coble between gage site 
ond recording equipment. 




Figure 15. Wiring Diagram for 
Fresh-water gage section. 



Ground Rod 



26 



k) Place all gage sections in water and remove the top gage 
section from the water 1 foot at a time, and mark the 
strip-chart accordingly. Continue with the remaining 
gage sections. 

1) Check the strip-chart record for linearity. 

m) If the chart is not linear, change the voltage out of the 
d.c. power module to 52 volts. 

n) Repeat steps g, h, i, j, k, and 1. A change in linearity 
should be found in the strip-chart recording. If linearity 
has improved, continue increasing the voltage in small in- 
crements and repeating steps g, h, i, j, k, and 1 until the 
desired linearity is obtained. If the linearity is worse, 
reduce the voltage in small increments and proceed with 
steps g, h, i, j, k, and 1 until good linearity is obtained. 

o) Turn off the strip-chart recorder using the switch on the 
programmer. 

p) Set the programmer to the desired recording program using 
screws in the program dial to provide a recording beginning 
at the selected hour or hours and for the selected number 
of minutes. 

q) Place the epoxy gage sections in the metal holder. 

r) Place magnetic tape recorder in operation. 

s) Gage is now in operation. 

c. Maintenance 

Maintenance of the gage involves changing the paper chart, 
refilling the ink reservoir, and checking the program units for proper 
timekeeping. 

The epoxy gage sections and the metal holder will require cleaning; 
frequency of cleaning will depend on local conditions. 

The lead tips on the epoxy sections will possibly grow a covering 
that looks like a hard powder. This covering will affect the gage 
accuracy and must be removed; use of sandpaper or steel wool may be re- 
quired. Reversal of the leads connecting the gage sections to the power 
supply sometimes changes the rate of covering, and may be tried if desired. 

Servicing of the recorders and programmers should follow instructions 
in the manufacturer's manuals. 



27 



Section III. PARALLEL-TYPE, STEP -RES I STANCE GAGE FOR SALT WATER 

1. Theory of Operation of Parallel-type, Step-Resistance Gage 

Due to the low resistance path created by a film of salt water 
on the epoxy wave gage sections, the gage design for fresh water cannot be 
used in the ocean. To compensate for the low-resistance, salt-water film 
and the increased electrolytic action in salt water, it is necessary to 
provide low resistance values in the wave staff and to use alternating 
current and low voltage in the sensing circuit. The circuit in Figure 16 
was evolved to permit the use of low-voltage, low-value resistors, and 
alternating current in the wave-sensing circuit. Analysis of this circuit 
(Figures 16 and 17) shows that a standard 115-volt, 60-cycle line is con- 
nected to a constant-voltage transformer. The output of the transformer 
is a constant 115 volts ± 1 percent for powerline variations between 95 and 
130 volts. This removes variations in the record that might be caused by 
a change in line voltage. Output of the constant-voltage transformer is 
applied to an autotrans former which provides a means for varying the volt- 
age applied to the wave-gage circuity. This feature of voltage adjustment 
permits calibrating the wave gage for full-scale indication on the strip- 
chart recorder. A voltmeter is used to monitor the voltage out of the 
autotrans former. 

The selected voltage from the autotrans former is connected to a 
stepdown transformer which further reduces the line voltage to a value 
suitable for wave-sensing resistors. The stepdown transformer also 
isolates the powerline from the wave staff. The secondary winding of the 
stepdown transformer is connected in series with the variable-resistance 
circuit provided by the parallel-resistor, water-conducting path, and the 
primary winding of a step-up transformer. The step-up transformer is 
identical to the stepdown transformer except that its windings are used 
in a reverse manner. 

Output voltage from the step-up transformer is applied to a bridge 
rectifier and low-pass filter to convert the varying amplitude (caused 
by changes in water level) of the 60-cycle a.c. source to a d.c. signal 
suitable for driving the recorder penmotor. The stepdown, step-up trans- 
former units and the rectifier- filter unit have fixed resistors incorpor- 
ated in them to aid in getting a linear signal from these units. 

This circuit utilizing the parallel resistance circuit of the wave 
staff and the low- voltage windings of the stepdown, step-up transformers 
is a low-voltage, current-sensitive circuit. Such a circuit must have 
low resistance electrical connections. It is mandatory that the step-up, 
stepdown transformers be placed physically close to each other and as 
near as possible to the wave gage staff sections. 

Design experience has evolved the resistor values for gages of 20 and 
25 feet as listed in Table V. These values operate with the other elec- 
trical component's listed in Table VI, and should provide a gage with good 
operational features and good linearity. Changes in components or re- 
sistor values may cause nonlinear gage response, and require circuit 
modifications. 

28 




OS 



E- 



too rt 
ni CO 



29 




30 



TABLE V 
RESISTOR VALUES FOR SALT-WATER PARALLEL STEP-RESISTANCE WAVE GAGE 



For 20-foot gage 



For 25-foot gage 



18.3 Ohms 


5 


each 


20.4 ' 


Top 


5 


each 


22.6 ' 


, Section 


5 


each 


24.7 ' 




5 


each 


26.9 • 




5 


each 


29.0 ' 




5 


each 


31.2 • 




5 


each 


33.4 ' 




5 


each 


35.6 ' 




5 


each 


38.0 • 




5 


each 


40.2 ' 




5 


each 


43.1 • 




5 


each 


45.4 • 




5 


each 


47.6 ' 




5 


each 


50.3 ' 




5 


each 


52.9 ' 




5 


each 


55.6 ' 


Bottom 


5 


each 


58.8 ' 


I Section 


5 


each 


62.1 




5 


each 


65.8 




5 


each 



9.9 


hms 


5 


each 


11.0 
13.0 


Top 
1 Section 


5 
5 


each 
each 


14.7 




5 


each 


16,5 




5 


each 


18.3 




5 


each 


20.4 




5 


each 


22.6 




5 


each 


24.7 




5 


each 


26.9 




5 


each 


29.0 




5 


each 


31.2 




5 


each 


33.4 




5 


each 


35.6 




5 


each 


38.0 




5 


each 


40.2 




5 


each 


43.1 




5 


each 


45.4 




5 


each 


47.6 




5 


each 


50.3 




5 


each 


52.9 




5 


each 


55.6 
58.8 


Bottom 
1 Section 


5 
5 


each 
each 


62.1 




5 


each 


65.8 




5 


each 



31 



TABLE VI 
COMPONENTS FOR FIVE-SECTION 25-FOOT PARALLEL RESISTANCE GAGE FOR SALT WATER 

1. Programmer, Tork Hourmaster Model 4100 1 ea. 

2. Voltage Regulator, Sola Type 20-13-030-1 1 ea. 
input 95-130 volts, output 118 volts 30 VA. 

3. Variable transformer, Superior Electric Co. Model lOB, input 1 ea. 
120 volts, single phase, 60 cycles output 0-132 volts 2.25 amps. 



4. a.c. voltmeter 0-150 volts, Triplett Model 337-S 1 ea. 






Filament transformer Thordarson No. T21F11 6.3 volts c.t. ( 2 ea. 
6 amperes. 



6^ Precision Resistors, wire wound, 1% Type TX-2212, manufactured ^ n 

by Precision Resistor Company, 109 U.S. Highway, Hillside, N.J./l25'e^ 

Values shown in Table V. L—^-^*""^ 

Scotchcast Resin #2, Minnesota Mining S Manufacturing Co. 42 lbs. 

Bar Solder, 50% tin, 50% lead. 6 lbs. 

9. Wire solid copper, plastic insulation AWG #14 25 ft. 

MfO Resistor, 500 Ohms, 10 watt 1 ea. 



/ll?) Selenium rectifier. International Rectifier #Q4B, 130V ^4 ea. 
Ky RMS, 100 MA 



V9 



12. j Capacitors, Sprague 155 P-156P Metallized-paper Tublar 



/4 eaJ 



4.0 mfd. 200 volts. ^ ^ 



/^^ 



13.^ Filter choke, Stancor C 1721 

8.5 Henrys 200 MA- V , ^ 

14. Box-Mounting receptacle Bendix Scinflex, RB 3102 #10-42214-2P 1 ea. 
Scintilla Division, Bendix Aviation Corp., Sidney, N. Y. 

15. Plain Gasket, used with box-mounting receptacle, Bendix 1 ea. 
Scinflex #10-40450-14 

16. Straight plug, Bendix Scinflex RB-3106 #10-42614-2S with 1 ea. 
#10-40908-141 back shell and #10-40457 Hex coupling nut 

and #AN-3057-^B cable clamp. 

17. Box, aluminum watertight 4 1/2" D x 6 1/2" W x 6 1/2" H 1 ea. 
Adalet #JP102, A Adalet Mfg. Co. Cleveland, Ohio. 



32 



TABLE VI (continued) 






1 


ea 


1 


ea 


1 


ea 


50 


ft 


110 


ft 



18. Utility box, metal 5" D x 6" W x 9" H. Black Crackle 2 ea. 
finish - Bud #CU 1099B. 

19. Switch SPST, Arrow Hart 5 Hegeman # 20994 BF 

20. Chart rewind. Brush Model #RA-2402-ll 

21. Strip-Chart Recorder Brush Model No. RD-2321-00 (order with 
following modifications: single channel operation and 50 mm 
chart width. Old style penmotor #BL 902 and Long Pen #BL 921, 

22. Wire solid copper, bare, tinned, AWG #18 

23. Cable 2-conductor #20 AWG with 2 high-strength 1 1/6" steel 
members. Neoprene outer sheath Marsh and Marine Mfg. Co., 
Houston, Texas, Type #TPSC. 

24. 4-conductor #14 AWG rubber covered. Length required to 
connect wave staff site to recording site. 

25. Plug amphenol #160-10 

26. Line cord a.c. Belden 17408-S 
Resistor, 11 Ohms 1% tolerance 10 watts IRC #AS-10 

28. Connector, male cable plug Amphenol type #80-MC2M 

29. Connector, female receptacle, Amphenol type #80 PC2F 

30. Relay DPDT, 115 volt, 60 cycles Potter Brumfield KRP HAG 

31. Potentiometer 2K-0hms Mai lory M2MPK, or equal 

32. Solder, 18 S.W.G. 60% tin/ 40% lead 

33. Socket, Octal, Amphenol #78RS8 

34. Connector, female 3-wire polarized type Harvey Hubbell 
"Twist Lock" #7484. 

35. Connector, male bage 3-wire polarized type Hubbell #7486 

36. Connector, male cap, 3-wire polarized type Hubbell #7485 

37. Connector, female base, 3-wire polarized type Hubbell #7487 

38. Cable, electrical, rubber covered, three-conductor AWG #18 
Belden type 8453 

39. Cord - Grip for rubber covered cable 0.500 - 0.625 diameter. 1 ea. 
aluminum, Pyle-National #DB-10 



3 


ea 


3 


^ 


^ 


ea 


-r 


ea 


2 


ea 




ea 




ea 




lb 




ea 




ea 




ea< 




ea, 




ea 


15 


ft 



40. Cable 2-conductor #18 AWG Belden #8452, or equal 



12 ft. 



NOTE: This list does not include gage mount, 



33 



The gage will operate in salt-water locations that have little or no 

change in salinity. If the gage is placed in locations having significant 

salinity changes, the wave record will vary in accuracy with the changes 
in salinity. 

2. Fabrication of a Parallel Step-Resistance Gage 

Fabricate the required number of S-foot epoxy gage sections as 
outlined in Figure 18. The top gage section will have the lower value 
resistor connected to the top five sensing plugs, and the resistors will 
progressively go higher in value until the highest value of resistors are 
connected to the five sensing plugs, and the resistors will progressively 
go higher in value until the highest value of resistors are connected to 
the five sensing plugs on the bottom gage section. The cable from each 
wave gage section (molded as part of the section) should not extend more 
than 10 feet from the top of the gage mount. The resistance in the gage 
cables and leads from the transformer unit connected to the gage cables 
and leads from the transformer unit connected to the gage cables are part 
of a low- voltage, current-sensitive circuit. The resistance of these 
connections must therefore be low; long leads or high resistance con- 
nections in this circuit must be avoided in order to provide best gage 
linearity. Wire size in the cables molded into the gage sections should 
not be smaller than 2-conductor No. 20 AWG in parallel. 

Fabricate the transformer unit as shown on Figure 19. Wire the 
transformer unit as shown on Figure 20. Be sure that all connections in 
this unit are well made and well soldered. This unit may be filled with 
a clear potting compound available from Dow Corning Company, their No. 182. 
If this unit is not filled, care should be taken to ensure that it is 
watertight . 

Fabricate the voltage control, rectifier-filter unit, and programmer 
as shown on Figures 10 and 21 and wire as shown on Figures 10 and 22. 

Strip-chart recorder chart speed may be modified, if desired, as 
outlined in Section VIII. Fabricate the signal connecting cable for 
the strip-chart recorder to the desired length using 2-conductor No. 18 
AWG cable as shown on Figure 11. 

Fabricate the metal gage holder to the required length shown in 
Figure 12. Suitable mounting brackets for the gage holder should meet 
local installation requirements. Mounting brackets must be strong enough 
to withstand the forces of wave action expected at the gage site. A 
bracket design that has been used on vertical piling is shown on Figure 
13 which may serve as a guide. 

Paint the gage holder with two coats of primer and two coats of any 
good commercial anti-fouling paint. Government agencies may use Government 
Services Administration GSA Stock No. GS8010-550-8305 and GS8010-290-6651, 
respectively. DO NOT PAINT THE GROUND ROD. Paint the gage sections that 
are below and at the water line with three coats of anti-fouling paint. 
Clean the sections of mold release prior to painting. DO NOT PAINT THE 
LEAD SENSING TIPS. 

Text resumes on page 40 
34 





35 



o 



o 



■^ I 4- -^ 



fl-4 -/t^- 






o 




o 





Figure 19. Transformer Unit for Salt -Water Gage 



36 




37 



S) & 




I ) 

1, 



mft 



1 L 



38 




a, 




3 




Ui 


<U 


ji 


03 


(1) 


I.'!) 


^ 




o 


d) 


a. 


1) 




C 


u 


CO 


n 


*-> 


M-l 


f> 




■ H 


a 


U1 


01 


<u 


u 


a: 



39 



3. Operation of Parallel-type, Step-Resistance Gage 

a. Installation 

Install the metal gage holder at the operation site. The 
holder should be installed so that about 6 to 8 feet are below mean lower 
low water and 17 to 19 feet out of the water. 

Provide a mounting for the transformer unit near the top of the gage 
mount but do not mount the transformer unit at this time. 

Install the 4-conductor No. 14 AWG cable between the gage holder site 
and the recorder site. 

Install the epoxy gage sections in the mount. 

Install the voltage-control programmer unit, the strip-chart recorder, 
chart take-up and magnetic tape recorder (if used) at their operating site. 
Connect these units and the transformer unit to the gage sections as shown 
on Figures 23 and 24. 

b. Calibration 

The accuracy of the recorded wave heights depends directly on 
the accuracy of the calibration of the gage. There are enough differences 
in each wave gage and each strip-chart recorder to require that each gage 
be individually calibrated. 

The ideal calibration would be that of raising and lowering the steel 
gage holder with the gage sections into the water in small increments and 
marking the strip-chart recorder accordingly. Usually, the lack of water 
depth, the manual process required, and the presence of wave action prevent 
such calibration. 

If many gages are to be calibrated, it may be desirable to provide a 
water basin about 24 inches in diameter with the required depth. A wave 
gage holder would be a permanent part of the calibration pit. The basin 
should be made of concrete pipe or other nonconducting material; use of 
a metal wall would cause inaccurate calibration of the gage. Water with 
proper salinity would be required. 

The procedure outlined below has been used and found satisfactory for 
calibration of staff -type gages. If feasible, a time of low wave action 
should be selected. 

If possible, keep the sections to be removed from the water first in 
the calibration process inside the steel gage holder. This will provide 
a more accurate gage calibration. If the water is deep enough, place two 
or three of the sections in the holder in the order that they are used in 
the gage. The section having the lowest value of resistors is on top, and 



40 



r 









1 «^^H^ 




2 <^^^ 




|=!4_f::Mv- 




24 t^^^^' 


; 


25 C^^ 






TRANSFORMER 
' UNIT 

(See Fig 23) 





4 conductor No. 14 or No. 16 
goge coble to recording 
equipment. 



Keep ttiese cables m as stiort 
lengtti as procticable. 



Epoxy Gage Sections 



Figure 23. Connecting Diagram for Parallel Step-Resistance Gage Section 



41 



POWER UNIT PARALLEL WAVE GAGE 



4 



rO 



I 



RECTIFIER UNIT •- 



To Transformer Unit 



J" 



riJ 



:fr 



PROGRAMMER 



^ 



I Manual Automatic Switcti 



VARIABLE 
TRANSFORMER 



115 Volt Lme 



4 



CONSTANT- *■ 
VOLTAGE 
TRANSFORMER 



STRIP-CHART 
RECORDER 

BRUSH MODEL 

RD-232I-00 

(Modified) 



^ ^ 



4 Conductor Cable- 



To 115 Volt Power Line 



MAGNETIC TAPE 
RECORDER 

CERC MODEL 
LW-I 



i" ''.'"' I 



CHART REWIND 

' BRUSH MODEL 

RD-2402-I I 



PROGRAMMER 



CZ) 



TRANSFORMER 
UNIT 

(See Figure 26) 



c^ 



Stiort Cable to Goge 

( See Figure 23 



Figure 24. Hookup Diagram for Parallel-type Step-Resistance Gage. 



42 



the succeeding sections are below it. When the section having the lowest 
value of resistors has been removed from the holder (in the desired cali- 
bration increments) , the other gage sections in the holder should be 
removed and a succeeding section put in the bottom; thus, all sections 
having the lowest resistors will be removed from inside the gage mount 
in succession during the calibration process. 

Calibration of the gage proceeds as follows: 

a) If a magnetic tape recorder is used, calibrate it with the 
strip-chart recorder as outlined on page 93. 

b) Remove the epoxy gage sections from the gage mount. 

c) Set the a.c. voltage-adjust control (autotrans former) on the 
voltage-control, rectifier-filter, programmer unit to its 
counterclockwise position. 

d) Apply power to the gage system and turn on the strip-chart 
recorder. 

e) Using the mechanical adjusting lever on the strip-chart recorder 
penmotor, adjust the .recording pen to the left side of the 
recording chart. 

f) Place all epoxy gage sections under water. The sections should 
be placed adjacent to the metal gage holder with the lead contact 
tips near the ground rod. The spacing between the tips and the 
ground rod should be nearly the same as that provided when the 
sections are inside the gage holder. 

g) Adjust the a.c. voltage control clockwise to provide full-scale 
movement of the strip-chart recorder pen. 

h) Repeat steps b, e, f, and g until zero and full scale are stable. 

i) Remove the top epoxy gage section from the water 1 foot at a 
time, and mark the strip-chart recording accordingly. Continue 
with the remaining gage sections. This is the calibration for 
the wave gage. If the calibration is nonlinear, clean the lead 
contact tips on the gage sections, check the electrical con- 
nections of the epoxy gage cables and the connection to the 
ground rod, and recalibrate. 

j) Mount the transformer unit near the top of the gage holder. 

k) Adjust the programmer to provide the desired recording periods 
of the wave gage. The programmer may be set to provide a re- 
cording beginning any hour for a selected number of minutes. 
Hours may be skipped by proper installation of the knurled 
screws in the programmer dial . 

43 



1) Place the epoxy gage sections in the gage holder, 
m) Gage is now in operation. 

c. Maintenance 

The gage sections and mount will require cleaning as dictated 
by local marine growth conditions. 

Repainting the gage mount and the lower epoxy sections with anti- 
fouling paint will extend the periods between cleaning. DO NOT PAINT 
THE GROUND ROD AND THE LEAD TIPS IN THE EPOXY GAGE SECTIONS. 

Recording charts and ink will require replacement at intervals in 
proportion to the recording program selected. 



44 



SECTION IV. RELAY-TYPE STEP-RESISTANCE GAGE FOR SALT AND FRESH WATER 



1. Theory of Operation of a Relay- Type Step-Resistance Gage 

The CERC relay-type step-resistance gage is designed for opera- 
tion where water salinity is expected to vary widely. This variation may 
approach that of fresh water or that of sea water with little change in 
gage operation. This gage holds calibration longer than other staff gages. 

The gage operates on the principle of water completing a circuit 
consisting of a power supply, a relay coil, and a switch (the switch is 
the water path) in series (see Figure 25 on the following page). 

The gage uses 125 relays for a 25-foot gage, each relay closing when 
its associated water contact is submerged. Only one power supply is 
required to operate all the relays. 

In order that the relays will operate in both fresh and salt water, 
it is necessary to modify the basic circuit in Figure 25 to the circuit 
in Figure 26. 

Electrolytic action in the water path makes it necessary to use 
alternating current in the gage circuit. However, when an a.c. relay is 
used, excessive relay chatter shortens relay life. This limitation makes 
it necessary to select a d.c. -operated relay, and subsequent selection of 
suitable rectifiers and filters for converting the a.c. gage-circuit 
potential to d.c. for relay operation. 

The basic relay circuit requires approximately 18 volts for operation 
in fresh water. When the same voltage is applied to the gage circuit in 
salt water, the voltage across the relay coil exceeds the coil voltage 
rating. To overcome the relay-coil overload, a 28-volt .07 ampere pilot 
lamp is installed to provide relay protection in salt water. In addition, 
this lamp will have a lower resistance value when not fully excited, thereby 
providing a correspondingly higher voltage to the relay coil when used in 
fresh water. 

The relays are connected to the copper contacts on the epoxy gage 
sections so that when the bottom contact on the gage is submerged, relay 
No. 125 is first to close, and when all contacts are successively submerged, 
relay No. 1 will be the last to close. 

The a.c. power-supply voltage to the relay circuit is adjustable by 
changing a jumper wire on a terminal strip on the power-supply chassis. 
The voltage should be adjusted to the minimum value that will provide 
positive relay closure at the location of the gage. For sea water, 9 to 
12 volts should be adequate; for most fresh water locations, 18 to 24 
volts should be adequate. 



45 



Relay 



I^XXAAA^* 



Ground Rod 



Cr-rry-Y^ jn Water 
Power 



Water Contact 
Water Surface 



Figure 25. Simplified diagram of relay-type, step-resistance gage. 



Silicon Rectifier 
INI692 



r-*f 



50MFD 
50 V 
♦ • 



Relay 



Pull in 5 volts 
6MA± IMA 
Drop out above 35 
ampere turns 



^ 



28 Volt - .07 omp. lamp 



1100 ohms 
1/2 wott 



6 to 24 V. odjustable 



ry-'rYyy-\ 



115 Volt 
60 Cycle 



Gage Ground 
Rod ^^-^ 



I I 

Water Contocf 



Wofer Surface 



Figure 26. Modified circuit for relay-type, step-resistance gage. 



46 



Gage response (relay response) to a rising water surface is prac- 
tically instantaneous. Gage response to a falling water surface is 
directly affected by the water salinity and cleanness of the epoxy gage 
sections. The epoxy gage sections should be kept as free of sea growth 
and dirt as local conditions will permit. Visual observations of wave 
action (counting the number of gage contacts from wave crest to trough) 
on the staff and comparison with the recorded wave record should provide 
evidence of proper gage operation. If local conditions permit, cleaning 
the epoxy gage sections and applying a coat of silicone wax to the epoxy 
will provide outstanding gage response. (Do not coat the copper contacts.) 

In addition to the relay-operating circuit, the gage contains the 
step-resistance recorder circuit which provides the signal to the recorder 
as dictated by the number of relays activated by the water level. 

The circuit in Figure 27 shows that when all relays are in the un- 
energized condition (no gage contacts submerged) , the step-resistance 
circuit is open and no voltage is available to the recorder input. When 
the bottom gage-contact is submerged and relay No. 125 operates, all re- 
sistors in the step-resistance network are in series with the d.c. power 
and recorder input. As each gage contact is submerged and the relays 
are operated, the resistors are short-circuited. This provides a higher 
voltage to the recorder as each relay closes (voltage to recorder is 
higher as the gage is submerged). Thus, the recorder will follow the 
change in water submergence of the wave staff. 

2. Fabrication of a Relay-Operated Step-Resistance Gage 

Fabricate the required number of 5-foot gage sections as required 
for the wave station. Table VII is a parts list for a relay-operated gage. 
Fabrication details of the sections are shown in Figure 28. Resistor 
values and cable color-code are in Table VIII. Cable lengths for the 
sections should be selected for the shortest length practicable to reach 
the location of the relay cabinet. Cost of the 25-conductor cable used 
in the fabrication of the epoxy sections is about $0.50 per foot, thus, a 
five-section gage will have a cable cost of $2.50 per foot between the gage 
mount and the relay cabinet. 

Fabricate the relay panels and relay power supply according to 
Figures 29 and 30, and wire them as shown in Figures 31 and 32. Mount 
these units in the relay cabinet as shown in Figure 33. 

Modify the strip-chart recorder paper speed (if desired) as outlined 
on pages 

Install three female 115-volt receptacles, one toggle switch and a 
line cord in Tork Timer Model 4100 as outlined on Figure 10. 

Fabricate a metal gage holder of proper length as shown on Figure 14. 
Fabricate gage-holder mounting brackets as local installation requirements 

Text resumes on page 59 



47 



RECORDER 



115 Volts 
60 Cycles 



TIMER 



Resistor 
No. I 



Resistor 
No. 2 



Resistor 
No. 124 



29-34 VOLTS 

DC. POWER SUPPLY 

(Regulated) 



# • — VWV\( — 



1500 otims 



Reloy No. I 



< — «^ 



Reloy No. 2 



< — - 



Relay No. 3 



< — » 



1—1 



Reloy No. 125 <Co"»^o"ed by bottom 
gage-contact ) 



Figure 27. Simplified Diagram for Relay-Gage 



48 




49 



H- +- +1+ + + + "t,--iri,i «.-. 



'^'"^''"^ 



+ t + + + t,±,i,i,-,.- 



NOTE Loyoul bose is l/4"lhick pleiigl' 
-f + + -f + + + + + + 



t + + + tiii,...- 



+ + -f + + + +1^ + + + -FTTT^ 

_^ 5" :^ '" r^'-'/'H 



^^rf ^ 



+ 



LAYOUT BASE 



iL 



-f 



+ 



4- 



^^^^' ^ 



411 holes 10 cleor 6-32 machine screws 1 No 28 drill ) 



Jr 



it 



4- 



-^t 2-1/2" 



ALUMINUM ANGLE PANEL MOUNT 



Note Ponel is o slondord 3-1/2 x 19 x 1/8 thick 

aluminum rock panel [ Hommertone groy finish) 

All holes to clear 6-32 mochme screws (No 28 drill) 



T 



^ 



T 



^ 



RELAY RACK PANEL 

.^I'H 5/8"R, |-l/2" I ^1/2" 




PLUG MOUNTING BRACKET 
Figure 29. Relay-panel layout for relay-type gage. 

50 







3/8" Dio hole 1/2" Dio hole 3/8" Dio hole 1/2" Dio hole 5/16" DIo, hole 



-^- 



2-1/8" 1 2-l/e"^ 2-1/8" -t 2-l/e' 



-2-1/4'^ — — f 2-1/4 




ZT 



Figure 30. Front panel and chassis drilling for relay-type gage 



51 



Q. 9> 



Q> 0» 



6 o 
< » 




52 




53 






















^ 


^ 


g 


§ 


g 


9 


§ 


g 


© 


^ 


@ @ 






» 




s 




8 




o 




8 


Volloge 
Control 

O e 






o 

Q- 

< 

o 
CE 


9 


o 
Q. 
00 

o 


s 

8 


o 

CL 
O 


9 


o 
Q- 

O 

o 
cc 


s 


o 

liJ 

o 


8 

8 


ll # 


5 

LlJ 

> 
1— 

z 
o 
cc 

Ll- 




fi 


a 


R 


8 


s 


S 


B 


8 


S 


a 


a 6 



















54 



TABLE VII 
COMPONENTS FOR FIVE- SECTION 25-FOOT RELAY STAFF GAGE 

1. Relay assembly consisting of Wabash magnetic coil No. L4988, 125 ea. 
or equal and Hamlin DRG-1 contact relay, or equal. Relay 

contact material is to be silver relay contacts to close 
at 3.85 ± 0.15 volts and 5.8 ± 0.2 milliamperes. Relay 
contacts to open at 3.3 ± 0.2 milliamperes. 

2. Machine screws steel nickel plated binder head, 6/32 x 1/2" 500 ea. 
long. 

3. Hookup wire (Alpha #1500 #24 Standard (any color) 500 ft. 

4. Nuts, steel nickel plated 6/32 x 1/4" 500 ea. 

5. Lockwashers, internal teeth #6 500 ea. 

6. Aluminum angle, 1" x 1" x 1/16" thick 10 ft. 

7. Aluminum angle, 1" x 2" x 1/8" thick 5 ft. 

8. Cable, 25-conductor - Marsh and Marine, Houston, Texas As required. 
Type XS CG 13R. 

9. Scotchcast Resin #2, Minnesota Mining § Mfg. Co. 42 lbs. 

10. Stainless Steel #316, round rod 1/4" O.D. 20 lbs, 

11. Plexiglas sheet 1/4" thick, 36 x 36 1 sheet 

12. Precision Resistors, wire wound 1%, Type TX-2212, 124 ea. 
manufactured by Precision Resistor Company, Hillside, N.J. 

(See Table V) 

13. Rotary Switch Centralab #PA-2000 1 pole, 2-12 position 1 ea. 
shorting type. 

14. Capacitor, Cornell-Dubilier ECSP 50-50 125 ea. 

15. Semiconductor rectifier, GE type 1N1692 500 ea. 

16. Resistor 1,100 Ohm 1/2 watt 5% IRC GBT 1/2 135 ea. 

17. Amphenol plug #26-4301-32 P 5 ea. 

18. Amphenol receptacle #26-4401-32S 5 ea. 



55 



135 


ea, 


125 


ea. 


1 


ea 


5 


ea 


5 


ea 


2 


ea 


5 


ea 



TABLE VII (continued ) 

19. Pilot Lamp #1829-28 V.O. 07 amp. 

20. Pilot Lamp Socket - Dialco #7-87 

21. Aluminum chassis Bud #AC-422, 5" x 13" x 3" 

22. Socket, 6 prong, Amphenol #78S6, with amphenol #3-24 
cable clamp 

23. Plug, Amphenol 86-RCP6 

24. Switch, SPST-12 Amps-AH § H #80607 

25. Panel aluminum, 3 1/2" H x 19" W, Bud #PA-1103-HG, 
Hammertone Gray. 

26. Panel aluminum, 5 1/4" H x 19" W, Bud #PA-1103-HG, 1 ea. 
Hammertone Gray. 

27. Cabinet - Panel 26 1/4" H x 19" W, Bud CR-1744 HG 1 ea. 
Hammertone Gray. 

28. Relay DPDT 115 v. 60 cycles Potter Brumfield KRPllAG 2 ea. 

29. Timer Tork Hourmaster #4100 1 ea. 

30. Cable, 2-conductor stranded, AWG #18 Type SV, Belden 8452 8 ft. 

31. Cable, 5-conductor stranded, 3-AWG 20, 2-AWG 18, Belden 8455 35 ft. 

32. Binding post, G.C. Electrocraft 33-270B 1 ea. 

33. Transformer, Stancor #P6429 1 ea. 
24. Solder, 18 S.W.G. 60% tin/40% lead 1 lb. 

35. Clip #UMC-10 Sprague Products Co. 130 ea. 

36. Wire, copper, solid-tinned AWG #18 100 ft. 

37. Potentiometer, 1,500 Ohms Mai lory M1.5MPK 1 ea. 

38. Terminal Block, H. H. Smith #602-5, General Purpose 1 ea. 
Bakelite. 



56 



TABLE VII (continued) 

39. Shaft locTc H. H. Smith #181 3 ea. 

40. Female Chassis receptacle amphenol #80-PC2F 2 ea. 

41. Male cable plug amphenol #80-MC2M 2 ea. 

42. Cord Belden #17460-S 2 ea. 

43. Plug amphenol #86CP8 with #324 cable clamp 1 ea. 

44. d.c. Power supply output volts 29.2 - 32.7, output current 1 ea. 
0.050 amps accuracy ± 0.05% Model M-31.5-050A, manufactured 

by Technipower, Inc. 18 Marshall Street, South Norwalk, Conn., 
Rep. Whitcomb Associates, 730 Deepdene Road, Baltimore, Md. 

45. Plug amphenol #160-5 1 ea. 

46. Potentiometer, 2,000 Ohms, Mallory M2MPK 1 ea. 

47. Strip-Chart Recorder Brush Model No. RD-2321-00. Order with 
following modifications: Single channel operation and 50 mm 
chart width. Old style Penmotor #BL902 and Long pen #BL 921. 

48. Chart take up drive Brush No. RA 2402-10 1 ea. 



NOTE: Less steel "H" Beam for holding epoxy gage sections. 



57 



TABLE VIII 



RESISTOR VALUES IN OHMS FOR 125-POINT RELAY GAGE 



13.5 


21.1 


37.7 


13.7 


21.5 


38.7 


13.9 


22.0 


39.8 


14.2 


22.4 


40.9 


14.4 


22.9 


42.1 


14.6 


23.4 


43.3 


14.9 


23.9 


44,5 


15.1 


24.4 


45.9 


15.4 


25.0 


47.3 


15.7 


25.5 


48.7 


15.9 


26.1 


50.2 


16.2 


26.7 


51.8 


16.5 


27.3 


53.5 


16.8 


27.9 


55.3 


17.1 


28.6 


57.1 


17.4 


29.3 


59.0 


17.8 


30.0 


61.1 


18.1 


30.7 


63.2 


18.4 


31.5 


65.5 


18.8 


32.2 


67.9 


19.1 


33.1 


70.4 


19.5 


33.9 


73.0 


19.9 


34.8 


75.8 


20.3 


35.7 


78.8 


20.7 


36.6 


82.0 



85.3 
88.0 
92.7 
96.7 

101. 

106. 

110. 

116. 

121. 

127. 

134. 

141. 

149. 

157. 

166. 

176. 

186. 

198. 

211. 

225. 

240. 

257. 

276. 

298. 

322. 



348 

379 

413 

452 

498 

550 

611 

683 

768 

871 

995 

1149 

1340 

1584 

1900 

2323 

2901 

3733 

4977 

5968 

10453 

17423 

34817 

104500 



CABLE-COLOR CODE FOR RELAY GAGES 



1 Brown 

2 Red 



9 Red 
10 Green 



19 Yellow 

20 Clear 



3 Brown 

4 Clear 



11 Red 

12 Blue 



21 Green 

22 Clear 



5 Red 

6 Orange 



13 Red 

14 White 



23 Blue 

24 Clear 



7 Red 

8 Yellow 



15 Red 

16 Clear 

17 Orange 

18 Clear 



25 White 

26 Clear 
(spare 

Conductor) 



58 



dictate. Brackets should be designed with adequate strength to support 
the gage holder during severe wave action. Figure 13 shows a type bracket 
that has been used successfully to support the gage holder on a vertical 
piling. Paint the gage holder and mounting brackets with two coats 
primer and three coats of a good grade commercial anti-fouling paint. 
Government agencies may obtain these from General Services Administration 
Stock No. GS8010-550-8305 and GSA Stock No. GS8010-290-6651 , respectively. 
Paint the underwater and waterline epoxy gage sections with three coats 
of anti-fouling paint. DO NOT PAINT COPPER SENSING TIPS. 

3 . Operation of Relay Type Step-Resistance Gage 

a. Installation 

Install the gage holder at the operating site. The holder 
should be installed so that about 6 to 8 feet are below mean lower low 
water and 17 to 19 feet out of the water. Install ground rod in holder. 
DO NOT PAINT GROUND ROD. 



Place epoxy gage sections in gage holder. 

Install relay cabinet, strip-chart recorder, chart rewind, programmer 
and magnetic tape recorder (if used) in operating location. 

Connect all units of the system as shown on Figure 34. 

Adjust tape recorder (if used) and strip-chart recorder as outlined in 
Section VII, paragraph 3. 

b. Calibration 



Calibrate the gage as follows: 

a) Apply power to the relay cabinet. Adjust the d.c. 

voltage from the regulated d.c. power module to 30.0 
volts. Turn on the strip-chart recorder, using the 
toggle switches located on the programmer and rear of 
recorder. 

b) Place the toggle switch on the relay cabinet marked 
"calibrate-operate" to the "calibrate" position. 

c) Place the rotary switch on the relay cabinet to the 
"operate" position. 

d) Adjust the strip-chart recorder pen to the left side 
of the chart paper using the lever on the side of the 
recorder penmotor . 



59 




60 



e) Place the rotary switch on the relay cabinet to posi- 
tion 5 (full-scale setting) . 

f) Adjust the linearity control on the front panel to the 
relay cabinet to provide full-scale pen movement on the 
strip-chart recorder. 

g) Move the rotary switch to its intermediate calibrate 
positions and mark strip-chart recorder accordingly. 

h) Check strip-chart recorder for linearity. If recording 

is not linear, adjust d.c. voltage of the regulated power 

module either up or down and repeat steps e, f, g, and 
h until linearity is obtained. 

i) Place rotary switch in "operate" position. 

j) Place the toggle switch marked "calibrate-operate" to 
the "operate" position. 

k) Raise or lower the epoxy gage sections in the water, 

and observe the strip-chart recording for a correspond- 
ing indication. 

A relay that is stuck closed will cause the recorder 
pen to remain at an up-scale position when all gage 
sections are removed from the water. A relay that 
does not close will be indicated by a jump in the 
recorder pen as the gage sections are lowered into 
the water. The terminal strip on the rear of the 
power-supply unit allows for adjustment of the voltage 
applied to the relay circuit. Salt-water locations 
require 9 to 12 volts for normal operations. Set 
voltage to the lowest value that will provide positive 
relay action and best relay fallout when the gage sec- 
tions are raised and lowered in the mount. A d.c. 
voltmeter may be used to measure the d.c. voltage 
across a relay coil that is in a closed position; this 
voltage should be about 5.5 to 6.5 volts. Greater 
relay voltage will cause the relays to remain closed 
when the gage sections are saturated with water, but 
with the gage contact out of water. This is due to 
conductivity of water film on the gage section. 
Excessive voltage will cause capacitor failure in 
the relay circuit. 

1) Adjust programmer to time recordings from the gage as 
desired. The programmer will provide a recording at 
the beginning of each hour for the selected number of 



61 



minutes. Hourly recordings may be deleted for any 
period by removing the knurled screws from the 
programmer dial . 

,m) Gage is now in operation. 



c. Maintenance 

Recorder chart and ink must be replaced in accordance with 
the recording program established. 

The epoxy gage sections, gage holder, and brackets will require 
periodic cleaning to remove sea growth caused by local conditions. 
Repainting of the gage holder and gage sections with anti-fouling paint 
will extend the periods of operation between cleaning, and retard marine 
growth. DO NOT PAINT IHE GROUND ROD OR THE METAL GAGE TIPS. 

Recorders should be serviced as outlined in the manufacturer's 
manuals. 

Periodic checking of the gage calibration is desirable. 



62 



Section V. PRESSURE-SENSITIVE GAGE 



1. Theory of Operation of Pressure-Sensitive Gage 

The pressure-sensitive wave gage operates on the principle that 

when a wave crest passes a given point there will be an increase in water 

depth, and with an increase in the height of the water column there will 
be an increase in the pressure at the bottom of the column. 

While a wave crest is not exactly equivalent to closed water column, 
the change in water level related to a wave crest or trough will cause a 
pressure change at the ocean bottom. If a pressure-sensitive device is 
placed near the ocean bottom, it will sense the pressure change caused 
by the wave. 

The signal from the pressure-sensitive device may be carried to a 
shore location over an electrical cable, and recorded on a paper-strip 
chart or magnetic tape recorder. Since the signal at the recorder is 
produced by the wave crest and trough, it is directly related to the wave. 

The pressure change produced by a wave train of constant amplitude 
and constant period will decrease as the pressure sensor is placed deeper 
and deeper in the water. If the wave period is made shorter, the pressure 
from the same wave height will also be reduced at a constant water depth. 
Ratios for conditions of pressure, depth, wave height and wave period 
have been established, and may be used to correct the recordings from a 
pressure-sensitive wave gage to provide a usable measurement of wave 
conditions. 

Ripples and small sharp surface changes will be filtered out of the 
wave record due to the pressure-period attenuation outlined above. This 
filtering will influence the wave spectra analysis so that there will be 
apparent differences when comparing spectra data taken at the same time 
and location with both pressure and staff gages. 

The change in tide at locations where pressure wave gages are used 
must be known. The increased water depths due to tide is, in effect, an 
increase in water depth, which must be used in correcting the wave record. 

For these reasons a pressure-sensitive gage is not an ideal device 
for gathering true data on waves. This gage is recommended only for those 
locations where the installation of a step-resistant staff-type gage is 
impracticable due to the cost of a mounting structure or where a mounting 
structure would cause a navigational hazard. 

The CERC-designed pressure-sensitive gage uses a Sylphon bellows 
that changes its length with an increase in pressure. The bellows move- 
ment is coupled to the core of a linear differential transfornjer by a 
permanent magnetic, steel ball, universal joint. 



63 



Movement of the core in the differential transformer produces a 
linear d.c. output voltage from the unit. This signal, representing the 
wave conditions, is amplified and applied to a strip-chart recorder. 

2. Fabrication of a Pressure-Sensitive Gage 

Fabricate the pressure-sensitive underwater unit as outlined on 
Figure 35. Table IX is a parts list for this gage. When soldering the 
end caps to the bellows, ensure that a watertight seal is provided and 
also prevent any solder from entering the corrugations of the bellows. 
The end for the bellows which is drilled for the magnet should be soldered 
to the bellows first. The magnet should then be inserted using an epoxy 
cement to ensure that it remains in place. The threaded end for the 
bellows is then assembled (soldered) using the minimum heat required for 
soldering. Too much heat could lower the efficiency of the magnet. It is 
recommended that edges of the bellows and the end caps be tinned prior to 
soldering into an assembly. It is also recommended that liquid stainless 
steel flux and solid wire solder, 60 percent tin and 40 percent lead, be 
used. 

When assembling the bellows unit to the main gage housing, use of 
Permatex No. 2 on threaded surfaces is recommended. The Permatex should 
be used sparingly, applying only a thin coat on both the male and female 
threaded parts. Prior to closing the space between the bellows and gage 
housing, remove any excess Permatex from inside the "0" ring; align the 
brass ring, which incloses the "0" ring, with the outside gage housing 
and tighten the housing firmly. Do not use the bellows as a purchase 
grip to tighten the assembly; vise grip pliers and a bench vise are 
recommended. 

The bellows should be assembled to the gage case, and the entire case 
and bellows tested for leaks prior to further assembly. This can be done 
by attaching a fitting to the cable end of the gage housing, filling the 
inside with air to about 30 pounds per square inch gage, and testing under 
water for bubbles. During this test, the bellows snould be blocked mechan- 
ically to prevent stress beyond its ratings. Blocking may be accomplished 
by using large plastic washers with small holes in their edges for accept- 
ing wire to hold the bellows in a blocked position. The washer used on 
the threaded end of the bellows will require a slot with an opening in 
order to place it above the bellows cap as shown in Figure 36. 

After testing the bellows and housing assembly, a short length of 
gage cable is fitted into the end of the gage housing and sealed with 
epoxy resin. Splicing the cable ends to a very fine flexible wire in the 
epoxy seal will aid later assembly of the transducer. Clean, but do not 
oil, the sliding core in the Sanborn linear differential transformer. 
Clean the core and center hole thoroughly. If the core does not slide 
freely in the transformer, return the transformer and core to the manu- 
facturer for repair or replacement. Any binding of the core will cause 
it to separate the steel ball from the magnet and render the gage useless. 
The steel ball and magnet provide a backlash-free universal joint that 
allows free movement of the core within the transformer. The core 



64 





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65 



TABLE IX 
LIST OF COMPONENTS FOR PRESSURE-SENSITIVE GAGE. MODEL BE-2 

1. Brass parts and magnet as shown on drawing, "Pressure Wave 1 set 
Gage Model BE-2. 

2. Bellows, 2-ply brass, 10 active corrugations, reference line 1 ea. 
No. 2137, Robertshaw-Fulton Controls Co., Fulton Sylphon 

Division, Knoxville, Tennessee. 

3. Transducer, d.c. differential transformer displacement, DCDT, 1 ea. 
Model 7DCDT-500, Sanborn Company, Transducer Division, 

Waltham, Massachusetts. 

4. Amplifier, Transistorized operational. Model TR-1 with mating 1 ea. 
amphenol connector suitable for chassis mounting, Boonshaft 

& Fuchs, Inc., Hatboro Industrial Park, Hatboro, Pennsylvania. 

5. Power supply, dual-output regulated, 60 volts d.c. Model 1 ea. 
60B10D-60B10D, Acopian Technical Company, Easton, Pennsylvania. 

6. Power supply, regulated-output 6.0 volts d.c, 0.375 amperes 1 ea. 
d.c. Model M-6. 0-0.375A, Technipower, Inc., South Norwalk, 
Connecticut. 

7. Socket, Amphenol, 11 prong #78511 1 ea. 

8. Chassis, aluminum 6" x 17" x 3", Bud AC-433 1 ea. 

9. Splicing kit, Scotchcast #82-Al 1 ea. 

10. Cord Set Belden 17408-SJ 2 ea. 

11. Connector, male cable plug, amphenol type #80-MC2M 2 ea. 

12. Connector, female receptacle, amphenol type 80PC2F 2 ea. 

13. Socket, octal, amphenol #78RS8 1 ea. 

14. Capacitor, Mallory, No. HClOlOO, 10,000 MFD lOVSP 1 ea. 

15. Plug, 3-prong, male with shell, amphenol #160-5 1 ea. 

16. Cord Set, Belden 17460-S 1 ea. 

17. Switch, toggle SPST, Arrow Hart d, Hegeman #20994-BF 3 ea. 

18. Socket, 3-prong female chassis mounting type amphenol 3 ea. 
#160-10 



66 



TABLE IX (continued) 

19. Time switch, Tork #4100 1 ea. 

20. Potentiometer, 10-turn, 200 K ohms, IRC type HD-150 1 ea. 

21. "Revodex" dial, IRC type RD-462 1 ea. 

22. Relay DPDT, 115-volt, 60 cycles. Potter Brumfield KRG HAT 1 ea. 

23. Binding Post, Superior type DF 30 GNC (Green) 1 ea. 

24. Binding Post, Superior type DF 30 WTC (WTiite) 1 ea. 

25. Binding Post, Superior type DF 30 BC (Black) 1 ea. 

26. Binding Post, Superior type DF 30 RC (Red) 1 ea. 

27. Capacitor, .047 MFD, 200 WVDC, Cornell-Dubilier Type ViMF 2S47 1 ea. 

28. Potentiometer 2,000 Ohms Mallory #M2MPK 1 ea. 

29. Nameplate, Brass 1 ea. 

30. Solder, 18 S.W.G. 60% tin/40% lead 1 lb. 

31. Resistor, 2,700 Ohms, wire wound, 1 watt, 5% tolerance 1 ea. 

32. Material for Concrete mounting block 

33. Strip-chart recorder. Brush #2321-00. Order with following 1 ea. 
modifications: single channel operation and 50 mm chart 

width. Old style penmotor #BL 902 and long pen EL 921. 

34. Chart rewind Brush #RA-2402-10 1 ea. 



67 




TOP WASHER 




Plexiglass 1/4 thick 



1/8" Dia. hole 



BOTTOM WASHER 



Figure 36. Washers for blocking bellows of pressure gage. 



68 



assembly should be placed in the linear differential transformer and 
placed in the gage barrel. Plastic washers must be placed between the 
transformer and the bottom of the barrel. These washers must be of 
varying thicknesses. The electrical output of the transformer should 
be zero or slightly negative when the transformer is resting on the 
washers in the gage barrel. 

Connect the differential transformer to a 6-volt d.c. source and 
measure the output with a high-impedence voltmeter set on a low range - 
about 3 volts. With the steel ball in contact with the magnet in the 
bellows chamber, with the bellows in free air (no pressure), and the 
transformer in firm contact with the plastic washers, the voltmeter 
should read volts, or slightly negative. Pressing the bellows with 
the fingers should show an upscale (positive) movement of the voltmeter. 
If the zero or slightly negative output voltage is not obtained on first 
trial, then the transformer and core assembly must be removed from the 
gage barrel and plastic washers of a different thickness tried until the 
correct reading is obtained. After the correct washers are selected, 
put together the spring assembly and "0" ring, and solder the transformer 
leads to the leads in the epoxy sealed cable-end of the gage housing. 
Fasten the cable portion of the gage housing to the gage barrel, using 
6 No. 10-32 screws. These screws should be tightened a little at a time 
to ensure equal pressure on all sides of the "0" ring seal. 

Fabricate the amplifier, power-supply unit as shown in Figure 37; 
wire the unit according to Figure 38. 

Construct the programmer by installing three 115-volt receptables, 
toggle switch and line cord on the timer as shown on Figure 10. 

Change the chart speed on the strip-chart recorder (if desired) as 
outlined in Section VIII. 

Fabricate a signal cable for the strip-chart recorder of the desired 
length using 2-conductor No. 18 AWG cable and connectors as shown on 
Figure 11. 

Fabricate a suitable underwater mount for the pressure unit. This 
mount should be high enough to keep the gage free of the ocean bottom; 
it should be large enough and heavy enough to remain in an upright posi- 
tion during periods of heavy wave conditions. To prevent metal erosion 
caused by galvanic action, dissimilar metals should not be used in contact 
in sea water. The brass pressure-unit must be mounted in plastic insulat- 
ing brackets to prevent metal erosion by galvanic action. Lifting eyes 
should be provided to lower the mount to the ocean floor and for attaching 
a marker buoy .(if required) . A simple concrete mount has been used for 
the gage in some locations (Figure 39) . If a marker buoy is used, the 
gage should be protected from the sagging and twisting of the buoy cable. 



69 



PROGRAMMED LINE CORD 



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70 



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Figure 39. Concrete Block for Mounting Pressure-Sensitive Gage. 



72 



3. Operation of Pressure-Sensitive Gage 

a. Calibration 

Perform the following steps in the given order for pressure- 
gage calibration: 

a) Connect the strip-chart signal cable to the amplifier- 
power-supply unit. 

b) Set the tide-capacitor switch to the "capacitor-out" 
position (switch contacts closed) . 

c) Apply power to the recorder and the amplifier-power unit. 

d) Adjust the d.c. voltage out of each 60-volt power supply 
to exactly 60 volts. 

e) Adjust the d.c. voltage out of the 6-volt power supply 
to exactly 6 volts. 

f) Remove power from amplifier-power unit and strip-chart 
recorder. 

g) Connect wave sensing-unit cable to the four binding posts 
on amplifier-power-supply unit. Be sure that the color 
code on the binding post has been carried to the same 
color code on the Sanborn linear-differential transformer 
inside the pressure-sensing unit. 

h) Set dial on the 10-turn variable resistor on the amplifier- 
power unit to its counterclockwise (lowest resistance) 
position. 

i) Apply power to amplifier-power unit and strip-chart 
recorder. 

j) Adjust pen on the strip- chart recorder to center of 
recording chart with lever on side of penmotor. 

k) Decide the maximum wave height to be recorded and divide 
by two. 

1) Lower gage 1 foot into still water and readjust recorder 
pen to center of chart paper with lever on side of pen- 
motor. 

m) Lower gage into water one-half of the wave height expected 
to be recorded. Value found in step k above. 



73 



n) Adjust 10-turn variable resistor clockwise until recorder 
pen moves to full scale. 

o) Repeat steps j, 1, m, and n above. 

p) Place tide-capacitor switch to "in" position (switch open) 

q) Tide capacitor will begin to charge, and recorder pen 
will slowly return to center of paper. When capacitor 
has charged as indicated by recorder pen returning to 
the center of the chart, quickly submerge the gage for 
the remaining one-half value of maximum wave height ex- 
pected. Recorder pen should again move to full scale on 
recorder chart. Quickly move gage to a depth of 1 foot. 
Recorder pen should move to opposite side of chart paper. 

r) To check gage linearity, place tide capacitor switch to 
"out" position. Place gage in 1 foot of water. Move 
recorder pen to side of chart paper with lever on side 
of penmotor. Submerge gage in 1-foot steps for full 
wave height. Slight adjustment of the 10-turn variable 
resistor may aid in setting linearity and full scale. 

s) Record the dial reading on 10-turn variable resistor 
and lock dial. 

t) Place gage in 1 foot of water. Re-center recorder pen 
on strip chart. Place tide-capacitor switch to "in" 
position. 

u) Gage calibration is complete; calibration may be plotted 
on graph paper for further use. 

If facilities are available, calibration of the gage may be carried 
out by using compressed air. Such facilities for calibration would in- 
clude an airtight chamber for housing the gage. This chamber should be 
large enough so that it does not mechanically hinder the gage bellows. 
A precision pressure gage with a suitable source of compressed air and 
air valves may be used to apply the same pressure to the air chamber as 
would be developed by the water depth. Calibration procedures would then 
be performed as outlined above, substituting equivalent air pressure for 
water depths. 

b. Installation 

Consideration should be given to the type cable required 
for use between the pressure-sensing unit and the recording equipment 
located on shore. If the surf zone is of sand, it may be possible to use 
4-conductor No. 14 AWG cable having a neoprene outer jacket. This type 
of cable should be taped parallel to an ordinary 1/2" diameter steel 
cable through the zone of wave action. The weight of the steel cable 



74 



should cause the cable to sink well into the sand in the surf area. Slack 
should be left in the cable to permit it to sink. 

If the cable must pass through a rocky (or impermeable) zurf zone, 
it may be necessary to use armored cable through the area where wave 
action will be directly on the cable. 

Cable used under water should be pressure-tested for leaks prior to 
use. Most cable suppliers will make the pressure test when requested. 

The short length of cable attached to the pressure-sensing unit 
should be spliced to the cable from shore using a 3-M No. 82A1 cable 
splicing kit. 

The wave-sensing unit should be mounted to its support using the 
plastic brackets shown in Figure 35. These brackets are required to 
prevent galvanic action from corroding the sensing unit. The gage cable 
should be taped firmly to the gage support at the point where the cable 
leaves the brass gage case. If this is not done, wave action will flex 
and break the cable. 

Laying the cable from the recording site to the offshore sensing 
point requires planning based on the gage location on the seabed. Coiling 
the cable in a figure 8 on deck of the boat, barge, or other vehicle will 
allow the cable to pay out without twisting. It may be desirable to lay 
the cable, and then splice the gage to the end after it is in place. The 
splice requires about 30 minutes to harden before placing under water. 

After the gage is in its operating location and the cable laid to the 
recording site, install the amplifier-power unit, the strip-chart recorder, 
chart rewind, programmer, and magnetic tape recorder (if used) and connect 
them as shown on Figure 40. The color code of the leads from the Sanborn 
linear differential transformer must be carried to the corresponding 
binding posts on the amplifier-power unit. 

After the gage system is connected as outlined above, apply power to 
the amplifier-power unit, strip-chart recorder, and magnetic-tape recorder, 
chart rewind, and the gage is ready for operation. The 10-turn variable 
resistor dial should be set to the value obtained in the calibration pro- 
cedure, and the tide-capacitor switch should be set in the "in" position 
(switch open) . 

When the gage is first placed in operation, the recorder pen will 
probably be off scale, since the tide capacitor is not in a charged 
condition. The off-scale condition of the recorder pen is normal, and 
the pen will slowly return to its normal position (center of chart) as 
the tide capacitor charges. The tape recorder signal meter will also be 
off scale as outlined above until the tide capacitor charges. 

The programmer should be adjusted to provide the desired wave-record 
program. The programmer will start the record at the beginning of each 



75 




76 



hour for a selected number of minutes. Any hour or hours may be omitted 
from the recording program by removing the knurled screws from the 
programmer dial . 

c. Maintenance 

The recording station will require servicing at regular in- 
tervals to change the strip-chart recorder-paper and fill the recorder 
inkwell. Also the programmer should be checked for timing accuracy. 

The wave-sensing unit should be raised and inspected at 6-month 
intervals to see whether it has been fouled by sea growth, and whether 
the entire gage has settled into the ocean bottom and bellows operation 
restricted. 



77 



Section VI. FABRICATION OF EPOXY GAGE SECTION 

To make epoxy wave staff sections, a suitable mold is required. The 
mold is fabricated by using a room-temperature curing silicone rubber. In 
order to conserve the silicone rubber, a close fitting aluminum container 
is fabricated as shown on Figure 41. A gage section pattern is also re- 
quired as shown on Figure 41, for either the relay-operated wave gage, or 
the other two types. The finish on the epoxy gage section will be that 
of the gage pattern; care should be taken to ensure a smooth surface. 

RTV-630 is available in gallon cans; the kits contain the silicone 
rubber in one container and the curing catalyst in another. The silicone 
rubber is used as the mold vehicle due to its releasing properties in 
removing the epoxy section when hardened. Place the gage pattern in the 
trough as shown in Figure 41, fill the space between the pattern and the 
trough with the RTV-630 and allow to cure as specified by the manufacturer. 
Use the amount of catalyst recommended by the manufacturer. Failure to 
do so will shorten the pot life and cause uneven cure of the mold. Avoid 
trapping air in the RTV-630 while stirring and pouring as bubbles cause 
holes in the completed mold. The trough should be filled to the brim. 
If excess is above the trough and gage pattern when curing is complete, 
it can be trimmed with a long sharp knife. When the mold is cured, remove 
the gage pattern and thinly coat the inside of the mold with vaseline. 
Recoat mold with vaseline between gage section moldings. 

Assembly components for the desired gage section on a jig outside the 
mold and check them electrically. After checkout insert the components 
in the mold as a unit and be sure that the metal gage sensing points are 
in the bottom of the mold. Align the gage cable with the mold so that it 
will be in the correct position when the section is completed. 

After the components have been placed in the mold, fill it with one- 
half the epoxy resin required for the gage section. Allow the section 
to cure 4 hours and fill the rest of the mold with epoxy resin. About 7 
pounds are required for one gage section. The resin is furnished in two 
parts and must be mixed in equal parts by weight just prior to using. Do 
not allow moisture in the resin during pouring and curing a.s it will cause 
the epoxy to turn white. Even a good healthy sneeze over the mold will 
turn the gage section white. 

When the epoxy has cured (overnight) remove the section from the mold, 
clean it thoroughly and recheck it electrically. Be sure the sensing tips 
are not coated with epoxy. 

The epoxy sections become brittle in cold weather and care should be 
exercised when handling to prevent breakage. 

The epoxy sections should be stored in a slotted wood board to keep 
them from warping. If a section becomes warped, it may be straightened 
by heating, placing in a straight position, and allowing to cool. 



79 




80 



Damaged sections may be returned to the mold and repaired by adding 
epoxy to the injured places. 

The epoxy sections may be repaired by drilling out the defective 
component, replacing the component and remolding the damaged section, 
using the original gage mold and new resin. 

If the gage mold is not used for several weeks, it may absorb moisture 
and cause the epoxy not to cure. Such moisture in the mold will also 
cause the epoxy sections to be white in color. Heating the mold for 
several hours should remove this moisture. 



81 



Section VII. MAGNETIC TAPE RECORDER FOR OCEAN-WAVE GAGES 

1 . Theory of Operation of Magnetic Tape Recorder 

No commercial tape recorders are available that could be modified 
to serve as an analog ocean-wave recorder for long periods of time. CERC 
found it necessary to design and build its own tape recorders. The mag- 
netic tape recorder Model LW-1 is designed to record ocean waves with 
periods of about 2 seconds through 100 seconds. Wave heights recorded 
full-signal on the tape recorder will be those from the wave gage that 
provide full-scale indication on the wave gage strip-chart recorder. 

The recording signal is a d.c. analog to the recording head. Line 
frequency is used as the recording bias to the tape head. Thus, the re- 
cording is similar to that used on a standard tape recorder for voice or 
music, although a higher frequency bias is used in a standard tape re- 
corder. However, at the wave period (frequency) at which the wave 
recorder operates, the line frequency (60 cycles) is more than adequate. 

The recording signal (wave-gage signal) from the three types of 
step-resistance wave gages is a to 30-volt d.c. analog. This signal is 
equal to zero submergence and full submergence, respectively, of the wave 
staff, thus the signal is proportional to the water level on the wave 
staff. The tape recorder has a 10,000 microfarad capacitor to remove the 
average d.c. signal from the wave-staff signal to prevent this average 
signal from reaching the recording tape head. This, in effect, removes 
the change in gage signal caused by tidal changes. Removal of this tide 
signal from the gage signal allows a wider dynamic range of the wave signal 
to be applied to the tape head, resulting in a better wave recording on 
the magnetic tape. 

The wave-gage signal from the pressure-sensitive wave gage has the 
tide component removed from the gage signal in the amplifier-power supply 
unit by a high-value capacitor in much the same manner as is done in the 
tape recorder. The output (wave-gage signal) from the amplifier-power 
unit is a d.c. analog of 15 +15 volts. This signal is proportional to 
the trough-to-crest wave height for the respective maximum wave height for 
which the pressure-sensitive unit is calibrated. This signal will produce 
full-scale movement of the recorder pen on the strip-chart recorder, and 
is used as the wave signal to the tape recorder. Therefore, the tide 
removal capacitor in the tape recorder is not required when the recorder 
is used with the pressure-sensitive gage. 

To operate the tape recorder with both types of wave gages (staff and 
pressure), one requiring tide removal, the other not, there is a switch in 
the tape recorder for bypassing the tide capacitor. It is labeled tide 
capacitor "in-out". 

The magnetic tape recorder may be operated with other wave-gaging 
systems provided those gages produce a d.c. analog signal proportional 



83 



to wave height. The d.c. analog should be 0-5 volts at 1 milliampere. 
Lower signals will attenuate longer period waves excessively. 

Bias signal amplitude, held constant by a constant voltage harmonic- 
neutralized transformer, is passed through a resistance-capacitor filter 
to further improve the wave form before it goes to the recording head. 

The recorder is designed to use Minnesota Mining and Manufacturing 
Company No. 428 magnetic tape 1/4 inch wide, on 1,250-foot reels. One 
reel of tape will record continuously for about 3 weeks. The tape speed 
used is one-half inch per minute. In normal recommended operation at CERC 
recording wave stations, the magnetic tape recorder operates continuously. 

Tape-recorder engineering design data was not available regarding the 
slowest speed that could be used. The minimum tape speed, tape-head gap, 
and bias frequency, needed to record 2-second waves in the field had to 
be developed in the CERC laboratory. 

To provide a section of tape long enough for analysis on the CERC 
spectrum analyzer, a recording must be at least 20 minutes long. While 
a 20-minute record may be analyzed, a 24-minute record is recommended. 

The recorder has a built-in calibrating signal (sine wave) with a 
period of 4 seconds. This signal, usually recorded for 30 minutes twice 
each day at 10 a.m. and 10 p.m. local standard time, is used to check 
recorder operation and to standardize input to the laboratory spectrum 
analyzer. The amplitude of the calibrating signal is adjustable to 
provide the same signal on the magnetic tape as the full-scale signal 
provided by the wave gage. The calibrating signal is programmed by a 
timer plugged into the recorder chassis. A switch is provided on the 
front of the tape recorder to permit the user to place the calibrating 
signal on the tape at his selection. This signal must also be 20 minutes 
or longer. 

The recorder does not have an erase head; magnetic tape used must be 
free of all recordings prior to use. When ordering, specify that tape 
shall be of virgin quality and free of all test recordings. Tape should 
be shipped in steel cans to aid in avoiding magnetic fields while in 
transit. 

Numbered, small, adhesive markers must be placed on the section of 
tape that is directly over the tape head when the tape is installed and 
just before it is removed. Additional markers should be similarly placed 
on the tape at significant times. Markers should be logged, listing the 
exact time of placement and any pertinent comments. These markers and 
the data logs are the only means of identifying the time of recorded 
wave data; their importance cannot be overemphasized. 

Two meters are incorporated in the recorder to adjust and monitor 
its operation. One has a zero center pointer, and indicates the ampli- 
tude of the waves at the tape recorder. A meter movement of 400-0-400 



84 



is selected for full signal wave conditions from the wave gage. The . 
other indicates the current in the record head from the bias signal, 
and is normally adjusted to provide a reading of 0.8 volt which corre- 
sponds to 8 milliamperes of bias current in the recorder tape head. 

2. Fabrication of Magnetic Tape Recorder 

Parts required for the CERC LW-1 tape recorder are listed in 
Table X. Details of fabrication are shown in Figures 42 through 45. 

The mechanical items should be assembled to the chassis and panel 
assembly. Particular care is required in aligning each electric motor 
shaft and the driven shaft. Use of 1/4-inch rod drilled with a 3/16- 
inch hole in one end through the panel bearings should aid in getting 
good alignment of the motor shafts. Use of a similar rod drilled with 
a 1/8-inch hole in one end should aid in aligning the calibrating signal 
drive motor (15 r.p.m.) with the synchro shaft. When the proper alignment 
is reached, the flexible couplings should receive the driven shafts 
without binding. Binding at this point will cause early failure of the 
flexible coupling. The panel shaft bearings should be cleaned, and given 
a drop of light oil during assembly. 

Wiring of the recorder is shown on the schematic diagram on Figure 
46. The wiring placement is not critical in obtaining proper operation. 
Good wiring practice is all that is required. 

The constant-voltage transformer is mounted in the left rear of the 
recorder cabinet. Input and output cables must be installed on the 
transformer to provide proper connection to the plugs on the rear of the 
recorder chassis. 

A signal cable for the tape recorder is fabricated to the desired 
length using 2-conductor No. 18 AWG and two amphenol No. 80-MC2-M 
connectors. 

Care is required in connecting the outer terminals of the three 
potentiometers on the front panel to provide increased signal conditions 
when the potentiometer shafts are turned clockwise. 

The tape-supply spool shaft uses a spring and washer assembly to 
provide tension to the tape. The tension of this spring should be 
adjusted to provide a very light pull on the unwinding tape. If too 
little tension is applied to the rewinding tape, the tape will skew on 
the capstan and foul the tape drive. Correct tension is just above that 
required to prevent tape skew. 

Ferrous parts used in the tape transport, including the recording 
head, should be demagnetized after assembly. If the tape head is mag- 
netized, or if the tape is placed close to a magnetized object, the tape 
recording will be of poor quality or may even be erased. 

Text resumes on page 93. 
85 



TABLE X 
LIST OF COMPONENTS FOR MAGNETIC TAPE RECORDER, LW-1 

1. Magnetic Tape Recording Head, Brush #BK-1250 

2. Motor, Hurst SM 1/2-1/2 RPM (Clockwise rotation) 

3. Motor, Hurst SM-15, 15 RPM, either right or left rotation 

4. Direct Current Microammeter - 500-0-500, Simpson Model #29 

5. A.C. Voltmeter 0-1 Volts - 1,000 ohms per volt, Simpson 
Model #49 

6. Cabinet-Bud, No. CR-1742-HG Gray Hammertone finish 

7. Transformer, Sola, No. 23-13-060 Harmonic neutralized type 

8. Transformer, Stancor P-6469 

9. Transformer, Stancor P-6134 

10. Transformer, Stancor PS-8416 

11. Potentiometer, wire wound, 5,000 ohms, Mai lory M5MPK 

12. Potentiometer, wire wound, 2,000 ohms, Mallory M2MPK 

13. Potentiometer, wire wound, 25,000 ohms, Mallory M25MPK 

14. Relay, Potter Brumfield, No. MRllA-DPDT- 115 volt, 60 cycles 

15. Autosyn, No. AY-201-3-B 

16. Cord Set, Belden #17460-S 

17. Cable, Belden #8452 

18. Resistor, wire wound, 1 watt, IRC, ±10%, 1,000 ohms 

19. Resistor, wire wound, 1 watt, IRC, ±10%, 1,200 ohms 

20. Resistor, wire wound, 1 watt, IRC, ±10%, 560 ohms 

21. Switch, SPST, Arrow Hart d, Hegeman, No. 20994-BF 

22. Rectifier - lN2070.or 1N1692 

23. Capacitor - 100 MFD-50 volts, Aerovox PRS 



86 



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TABLE X (continued) 

24. Resistor - 1 watt, wire wound, IRC - 2,000 ohms 2 ea. 

25. Capacitor - Paper 2MFD, 200 volts - Aerovox P82Z 4 ea. 

26. Idler, Wheel, Walsco, No. 1488 1 ea. 

27. Coupling, Millen No. 39016 2 ea. 

28. Spring-General Cement, No. H412-F 1 ea. 

29. Snap Button-Hole Plug, General Cement, H308-F 3 ea. 

30. Chassis, Aluminum 10" x 17" x 4", Bud AC 427 1 ea. 

31. Socket, Octal, Amphenol 78RS8 1 ea. 

32. Plug, Harvey Hubbell No. 7485 1 ea. 

33. Plug, Harvey Hubbell No. 7484 1 ea. 

34. Plug, Harvey Hubbell No. 7486 1 ea. 

35. Plug, Harvey Hubbell No. 7487 1 ea. 

36. Connectors, Amphenol, male plug 80-MC2M 2 ea. 

37. Connectors, Amphenol, female receptacle 80-PC2F 1 ea. 

38. Capacitor, Mallory, No. HClOlOO, 10,000 MFD, lOVSP 1 ea. 

39. Bearing, Bost-Bronze, oil- impregnated bronze, Boston gear 3 ea. 
No. FB-46-6 

40. Resistor 111 ohms ±1%, 1 watt, Precision Resistor Company 1 ea. 
109 U.S. Highway, Hillside, New Jersey. 

41. Plug 3-prong male with shell amphenol #160-5 1 ea. 

42. Bearing assembly TV. Contro-Roller as per Columbia Wire 1 ea. 
Supply Co., 2850 Irving Park Road, Chicago, Illinois. 

43. Nameplate, brass (as desired) 1 ea. 

44. Grommets, Smith 2174 2 ea. 



NOTE: List does not contain raw material for machining tape guides, tape 
capstan, flexible coupling for synchro, nuts, bolts, hookup wire, 
or terminal strips. 



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The spring for tensioning the rubber idler against the tape capstan 
should be designed to place a firm pressure on the tape. If the tension 
is insufficient, it will allow the tape to be pulled through the capstan 
roller by the take-up reel, resulting in a tape speed too fast for proper 
recording. 

If the tape recorder is turned off, the capstan roller must be 
backed off from resting on the capstan. If the roller is allowed to 
stand on the capstan with pressure, the rubber roller will indent perma- 
nently and be rendered useless. Removal of pressure on the capstan is 
accomplished by placing a pin through the roller bracket into a hole 
drilled in the front panel. 

The recorder requires a timer for placing the internal calibration 
signal on the tape automatically. Figure 47 shows assembly and wiring 
of this timer. The timer cable plugs into the octal socket on top of the 
tape-recorder chassis. Calibration of the tape recorder requires a 
calibration unit which is fabricated according to Figure 48. Parts 
required are listed in Table XI. 

3. Calibration and Operation 

The wave signal from the gage must have an amplitude that will 
provide a current of 0.8 milliampere through the magnetic tape head. 
The voltage level from the wave gage should be greater than 5 volts for 
the tide capacitor in the tape recorder to have an adequate time constant. 
The wave signal from the CERC wave gages is more than that required, and 
the signal level is reduced and adjusted by the potentiometer in the lower 
center adjusting-port in the front panel of the tape recorder. See 
Figure 49. 

The bias frequency to the tape head must be 8.0 milliamperes, and 
is adjusted by the potentiometer located through the port on the bottom 
right from center panel position. 

The internal 4-second period calibration signal also must provide 
0.8 milliampere through the magnetic tape head. This signal will be 
indicated by the left meter on the tape recorder panel. The meter will 
swing 400-0-400 microamperes when properly adjusted. A centering control 
on the inside chassis of the recorder is provided to center the calibra- 
tion signal on this meter. 

Calibrate the tape recorder by the following steps: 

a) Turn all controls recessed in the three ports in the bottom 
center of the recorder panel to their counterclockwise 
positions . 

b) Set the centering control on the recorder chassis to its mid- 
point of rotation. 

Text resumes on page 98 
93 



TORK TIMER 
Model No. 4100 Hourmoster 




Clock Motor Winding 



Pin Nunnbers 2 



3 5 



Switch Contacts 



4 Conductor No. 18 AWG 
Belden 8454 - 8 feet long, 
(or length as desired ) 



I I I I 



Amphenol mole plug 8 pin octal 

No. 86CP8 with cap amphenol No. 3-24 



Figure 47. Calibration signal timer for magnetic tape recorder. 



94 



note: Ports mounted on Bud 
Chassis No. AC-431 




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Amphenol 
No. 80-PC2F 



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DPDT 
Switcti 



->^pf<^^ 



1500 Ohms 

Variable Resistor 

Mallory M 1.5 MPK 



/ 



18 Volts D.C. output 



ACOPIAN CONSTANT 
VOLTAGE POWER SUPPLY 

Model I8A05 



On and Off Switch 



To 115 Volts 
60 Cycles 



Figure 48. Diagram of Calibration Unit 



95 



TABLE XI 
PARTS REQUIRED FOR A CALIBRATION UNIT FOR CALIBRATION OF A TAPE 
RECORDER WITH A STRIP-Clia,RT RECORDER 

1. Power Supply Output, 18 volts d.c. at 50 milliamperes 1 ea. 
input 115 volts, 60 cycle, Acopian Technical Company, 

927 Spruce Street, Easton, Pennsylvania, Model H 18A05, 
or equal. 

2. Potentiometer 1,500 Ohms, 4 watt, Mallory M1.5MPK, or equal. 1 ea. 

3. Switch DPDT, Arrow Hart 5 Hegeman #20905 FR, or equal 1 ea. 

4. Female receptacle, Amphenol #80-PC2F, or equal 2 ea. 

5. Chassis aluminum, 4" x 6" x 3" Bud AC-430, or equal 1 ea. 

6. Line cord, Belden, 17408S, or equal 1 ea. 

7. Knob Nation Co. HR, or equal 1 ea. 

8. Switch SPST, A-H ^ H #20994LH, or equal 1 ea. 

9. Rubber grommet for line cord 1 ea. 



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97 



c) Apply power to the recorder, and set the "calibrate-signal" 
switch on the front panel to the "calibrate" position. 

d) Adjust the right adjusting potentiometer on the front panel 
to provide a reading of 0.8 volts on the right panel meter. 

e) Adjust the left potentiometer on the front panel to provide a 
swing of 400-0-400 on the left meter. If the meter does not 
swing equally on each side of zero, adjust the centering 
control on the recorder chassis to obtain equal movement of 
the meter pointer on each side of center. Due to the inertia 
of the meter movement, the meter pointer will not provide an 
accurate indication of the actual current in the meter. To 
get the precise peak pointer-movement of the meter, it is 
necessary to stop the synchro shaft at its peak signal point 
of rotation. To do this, set the switch on the chassis near 
the synchro to the "calibrate" position, and grasp the coupling 
attached to the synchro shaft and turn it manually to provide 
peak indication on the left panel meter. Adjust the panel 
control for the proper 400-0-400 movement of the meter corre- 
sponding to the physical location of the synchro shaft that 
produces maximum swing of the meter. The centering control 
may require further adjustment at this time. Adjustment of 
the oatihration signal -is very important as it is used to 
standardize the wave gage signal and the spectrum analyzer 

in the CERC laboratory. Return the calibrate switch near the 
synchro to its "operate" position when the above adjustment 
is completed. 

f) Connect the signal cable from the magnetic tape recorder and 
the signal cable from the strip-chart recorder to the calibra- 
tion unit as shown on Figure 50. 

g) Set the voltage-control potentiometer on the top of the cali- 
bration unit to its counterclockwise position. 

h) Apply power to the tape recorder and strip-chart recorder, and 
set the calibrate switch on the front panel to "off". 

i) Adjust the strip-chart recorder pen to the center line on the 
recording chart using the manual control on the penmotor. 

j) Place the tide-capacitor switch on the tape recorder chassis to 
the "out" position (switch closed) . 

k) Apply power to the calibrate unit, and adjust the strip-chart 

recorder pen for full-scale indication (one-half of chart width) 
using the voltage-control potentiometer on the calibration unit. 

1) Adjust the bottom center control on the tape recorder panel to 



98 



To 115 Volt 60 Cycle 
Power Line 



To 115 Volt 60 Cycle 
Power Line 



MAGNETIC TAPE 
RZCORDER 



Magnetic Tope Recorder 
Signal Cable 



STRIP CHART 
RECORDER 



Recorder Pen Motor 
Signol Cable 




To 115 Volt 60 Cycle 
Power Line 

} 



Figure 50. Block Diagram of Calibration hookup. 



99 



provide an indication of 400 microamperes on the left mag- 
netic tape recorder meter. 

m) Move the polarity-reversing switch on the calibrate unit 
to its other position. The strip-chart recorder pen should 
indicate full scale on the other side of the chart paper, 
and the magnetic tape recorder signal meter should indicate 
400 microamperes on the opposite side of zero from that 
found in 1) above. 

n) Readjust the bias meter signal to 0.8 volt. When switching 
from "operate" to "calibrate", the bias meter will change 
slightly; this is normal, and will not affect recorder 
operation. 

o) The magnetic tape recorder is now calibrated for full-scale 
recording of the signal that produces full-scale movement 
of the strip-chart recorder pen. Since the strip-chart 
recorder pen indicates the maximum wave height produced 
by the wave gage, the magnetic tape recorder is also so 
calibrated. 

Since all strip-chart recorders do not have the same sensitivity, 
the wave-gage circuitry is adjusted to overcome this deficiency when the 
wave gage is calibrated. Therefore, the calibration of the magnetic tape 
recorder must be mated with the calibration of the strip-chart recorder 
with which it operates. 



100 



Section VIII. MODIFICATION OF STRIP-CHART RECORDER SPEED 



The slowest speed of the chart on the recorder as received from the 
manufacturer is 5 millimeters per second or about 12 inches per minute. 
To conserve chart paper and lengthen the time between visits to the wave 
recording station, it is desirable to change the chart speed to a lower 
value. 

Three lower chart speeds can be provided for the recorder with 
fairly simple changes in the gears. These changes will provide a basic 
chart speed of 2.5 millimeters per second, 1.25 millimeters per second, 
or 1.0 millimeter per second. 

Recorder paper comes in rolls 300 feet long on GSA schedule from 
Judson Bigelow, Inc., 12-12 44th Avenue, Long Island City, New York, 
Chart No. RA-2911-30 JB. With the recorder operating for 7 minutes each 
4 hours and the reduced chart speed of 2.5 millimeters per second, a 
300-foot roll will last about 14 days. If different frequency recording 
periods are desired, the time span for one roll may be calculated. 

If the recorder is modified to a slower chart speed, wave crests 
will appear closer together on the chart. A sample of wave periods, 
using sine waves, on a recorder chart with speeds of 2.5 millimeters, 
1.25 millimeters, and 1.0 millimeter per second are shown on Figures 
51, 52, and 53. 

To modify the recorder chart speed, proceed as follows: 

a) Fabricate the required gear assemblies and parts for the 
selected chart speed as shown on Figures 54 through 56. 

b) Remove the recorder pen. 

c) Remove the chart platen. 

d) Remove the chart payout guide and paper tear-off unit . 

e) Remove the chart driving roller, taking care not to lose the 
two brass spacers on the ends of the roller. 

f) Remove the chart speed-shift knob assembly. A thin knife blade 
"in the side of the main drive-shaft slot will accomplish this. 

g) Remove the snap spring on the main drive shaft. Observe the 
spacing between the spring and the recorder frame, and retain 
this distance when recorder is re-assembled. 



101 




5- Second Wave Period 




10- Second Wave Period 




20- Second Wave Period 
Figure 51. Wave records with chart speed of 2.5 millimeters per second 



102 




5- Second Wave Period 




10-Second Wave Period 




20- Second Wave Period 
Figure 52. Wave records with chart speed of 1.25 millimeter per second. 



103 




5-Second Wave Period 




10-Second Wave Period 




20-Second Wave Period 



Figure 53. Wave records with chart speed of 1.0 millimeter per second. 



104 



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107 



h) Ranove nuts from secondary gear-cluster shaft. 

i) Loosen set screw in collar on left side of recorder main 
drive shaft. 

j) Remove the side frame of the recorder from the recorder base 
opposite from the motor. 

k) Remove large gear from left side of main gear shaft. 

1) Remove spacer which holds the smallest gear on main 
drive shaft. 

m) Place new gears and spacers on main drive shaft and on 

secondary gear-cluster shaft as shown on Figures 57 and 58. 

n) Re-assemble recorder, and tighten setscrews in spacers and 
new drive gear. 

o) If gear assembly binds when re-assembled, some hand-fitting 
of the spacers may be required. 

The gear train should run freely when it is properly adjusted. 

Lubricate the shafts and gear trains when reassembling. The re- 
corder gear assembly before and after modification is shown on Figures 
57 and 58. 



108 




109 



Section IX. ANALYSIS OF OCEAN WAVE GAGE RECORDS 

1 . Step-Resistance Wave Gages 

Strip-chart recordings taken at CERC ocean wave recording sta- 
tions are analyzed for significant wave height, Hs, and significant wave 
period, Ts . 

The visual method used in analyzing strip-chart recordings (as opposed 
to automatic magnetic tape analysis) for a significant wave height and wave 
period follows: 

a) From a chart run (normally 7 minutes), select as nearly as 
possible the minute with a wave train which contains most of 
the highest and most uniform waves. 

b) Determine the period of the wave selected in step a) by using 
the wave-period template according to instructions (Figure 59). 
When the wave period on the chart falls between two of the 
periods shown on the template, the analyst may approximate 
what he considers will be nearest to the exact period. For 
example, if the period is about halfway between the 5-second 
template and the 6-second template, then the period is about 
5.5 seconds. 

c) Use the listing below to determine which wave should be 
measured to get the approximate significant height of the 
waves. The wave-height template will aid in determining 
which wave is to be measured for height. 

Wave period (seconds) Wave to measure 

3 3rd highest 
3.5 3rd highest 

4 2nd highest 

5 2nd highest 

6 2nd highest 

7 2nd highest 

8 or longer 1st highest 

d) With the proper wave-height template (Figures 60 and 61), 
determine the height of the wave given by step c) by finding 
the rectangle on the template whose top line comes nearest to 
to the crest when the bottom line is on the preceding trough. 
The wave height, in feet, is indicated by the number on the 
rectangle. 

e) Records with wave heights less than 1/2 foot are listed on the 
compilation sheet (Figure 62) as calm - without listing the 
wave height. However, the significant wave period for such 
records is determined and is indicated on the compilation 
sheet . 

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Figure 61. Sample of wave-height template (Fabricate from clear acetate 

using proper gage calibration.) 

114 



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ATLANTIC CIT Y N J 



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115 



2. Pressure-Sensitive Gages 

Due to the depth-period attenuation present when wave record- 
ings are taken using a pressure sensor placed near the ocean bottom, 
the recordings will require a correction factor to obtain a true wave- 
height reading. 

To obtain the true wave-height data (significant height and sig- 
nificant period), use the following procedure: 

a) Determine the significant height and period outlined in the 
in the method for step-resistance gages. 

b) Using the significant period refer to Figure 63 and find the 
line representing this wave period. 

c) Determine the water depth at the time the recording was taken. 

d) Intersect the water depth and wave period on the period curve. 

e) Read the K (response) factor below the point of intersection. 

f) Divide the significant height (found in a) above) by the 
K factor to obtain a corrected wave height. 

The curves apply only to a wave gage mounted on the ocean bottom. 
If the gage is mounted near the surface, additional curves will be 
required. Data for preparing these curves (K factor) is available on 
page D2 and Tables D-1 and D-2 of CERC Technical Report No. 4, "Shore 
Protection. Planning and Design", 3rd Edition, 1966. 



116 









































































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117 



UNCLASSIFIED 



Security Classification 



DOCUMENT CONTROL DaTA -R&D 

(Security claasiltcation of title, body of abstract and indexing annotation must be enterod whon tho 



all report l« clatallled) 



INS ACTIVITY (Corporate author) 



Coastal Engineering Research Center (CERC) 
Corps of Engineers, Department of the Army 
Washington, D. C. 20016 



REPORT SECURITY CLASSIFICATION 

UNCLASSIFIED 



2b, CROUP 



REPORT TITLE 



CERC WAVE GAGES 



4. DESCRIPTIVE NOTES (Type of report and Incluelve datea) 



B. AUTHOR(Sl (Flrat name, middle Initial, laat name) 

Leo C. Williams 



e- REPORT DATE 

December 1969 



7a. TOTAL NO. OF PASES 

124 



76. NO. OF REFS 





CONTRACT OR SRANT NO. 



6. PROJECT NO. 



ORISINATOR'S REPORT NUKTBERIS) 



Technical Report No. 30 



9b. OTHER REPORT NO(3> (Any other numberB that may be aaalgned 



10. DISTRIBUTION STATEMENT 

This document has been approved for public release and sale; its distribution 
is unlimited. 



11. SUPPLEMENTARY NOTES 



ITARY ACTIVITY 



13. ABSTRACT 



CERC has used wave gages to gather prototype wave data since 1948. Two 
basic types of gages are now used in the field - the step-resistance staff 
gage and the underwater pressure-sensitive gage. CERC has developed three 
types of step-resistance staff gages - a series type for use in fresh water, 
a parallel type for use in salt water, and a relay-operated type for use in 
either fresh or salt water or in water where wide changes in salinity occur. 
The pressure gage can be used in water of any salinity. The series and 
parallel gages have an accuracy of ±5 percent plus the spacing of one sensor 
increment. The relay gage has an accuracy of ±2 percent plus the spacing of 
one sensor increment. The accuracy of the pressure-sensitive gage is not as 
precise as that of the step-resistance gages. The report describes each gage 
and the theory of operation, details of fabrication, steps for calibration 
and installation, and requirements of maintenance. 



DD 



FOIM 

( MOV •• 



1473 



U.XCLASSIFIED 
Security ClatsificaUon 



UNCLASSIFIED 



Security Classification 



Ocean-wave gages 
Oceanographic instrumentation 
Step-resistance wave gages 
Strip-chart wave records 
Magnetic tape wave records 
Wave-record analyzer (magnetic tape) 



UNCLASSIFIED 



Seciuity Classification 





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